B7-DC variants immunogenic compositions and methods of use thereof

ABSTRACT

Compositions and methods for costimulating T cells (i.e., increasing antigen-specific proliferation of T cells, enhancing cytokine production by T cells, stimulating differentiation ad effector functions of T cells and/or promoting T cell survival) are provided. Suitable compositions include variant B7-DC polypeptides, fragments and fusion proteins thereof. Variant B7-DC polypeptides have reduced binding affinity for the inhibitory PD-1 ligand and substantially retain the ability to costimulate T cells. Methods for using variant B7-DC polypeptides to stimulate immune responses in subjects in need thereof are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of and priority to U.S. Ser. No.60/949,785 filed on Jul. 13, 2007.

GOVERNMENT SUPPORT

This invention was made with government support awarded by the NationalInstitutes of Health under Grant Number R01 CA85721. The United Statesgovernment has certain rights in this invention.

FIELD OF THE INVENTION

This invention relates to compositions and methods for modulating T-cellactivation, in particular to compositions and methods for enhancingT-cell activation.

BACKGROUND OF THE INVENTION

Antigen-specific activation and proliferation of lymphocytes areregulated by both positive and negative signals from costimulatorymolecules. The most extensively characterized T cell costimulatorypathway is B7-CD28, in which B7-1 (CD80) and B7-2 (CD86) each can engagethe stimulatory CD28 receptor and the inhibitory CTLA-4 (CD152)receptor. In conjunction with signaling through the T cell receptor,CD28 ligation increases antigen-specific proliferation of T cells,enhances production of cytokines, stimulates differentiation andeffector function, and promotes survival of T cells (Lenshow, et al.,Annu. Rev. Immunol., 14:233-258 (1996); Chambers and Allison, Curr.Opin. Immunol, 9:396-404 (1997); and Rathmell and Thompson, Annu. Rev.Immunol., 17:781-828 (1999)). In contrast, signaling through CTLA-4 isthought to deliver a negative signal that inhibits T cell proliferation,IL-2 production, and cell cycle progression (Krummel and Allison, J.Exp. Med, 183:2533-2540 (1996); and Walunas, et al., J. Exp. Med.,183:2541-2550 (1996)). Other members of the B7 family include B7-H1(Dong, et al., Nature Med., 5:1365-1369 (1999); and Freeman, et al., J.Exp. Med., 192:1-9 (2000)), B7-DC (Tseng, et al., J. Exp. Med.,193:839-846 (2001); and Latchman, et al., Nature Immunol., 2:261-268(2001)), B7-H2 (Wang, et al., Blood, 96:2808-2813 (2000); Swallow, etal., Immunity, 11:423-432 (1999); and Yoshinaga, et al., Nature,402:827-832 (1999)), B7-H3 (Chapoval, et al., Nature Immunol., 2:269-274(2001)) and B7-H4 (Choi, et al., J. Immunol., 171:4650-4654 (2003);Sica, et al., Immunity, 18:849-861 (2003); Prasad, et al., Immunity,18:863-873 (2003); and Zang, et al., Proc. Natl. Acad. Sci. U.S.A.,100:10388-10392 (2003)). B7-H1 and B7-DC are ligands for PD-1, B7-H2 isa ligand for ICOS, and B7-H3 remains at this time an orphan ligand(Dong, et al., Immunol Res., 28:39-48 (2003)).

B7 family molecules are expressed on the cell surface as homodimers witha membrane proximal constant IgC domain and a membrane distal IgVdomain. Receptors for these ligands share a common extracellularIgV-like domain. Interactions of receptor-ligand pairs are mediatedpredominantly through residues in the IgV domains of the ligands andreceptors (Schwartz, et al., Nature Immunol., 3:427-434 (2002)). Ingeneral, IgV domains are described as having two sheets that eachcontain a layer of β-strands (Williams and Barclay, Annu. Rev. Immunol,6:381-405 (1988)). The front and back sheets of CTLA-4 contain strandsA′GFC′C and ABEDC,″ respectively (Ostrov, et al., Science, 290:816-819(2000)), whereas the front and back sheets of the B7 IgV domains arecomposed of strands AGFCC′C″ and BED, respectively (Schwartz, et al.,Nature, 410:604-608 (2001); Stamper, et al., Nature, 410:608-611 (2001);and Ikemizu, et al., Immunity, 12:51-60 (2000)). Crystallographicanalysis revealed that the CTLA-4/B7 binding interface is dominated bythe interaction of the CDR3-analogous loop from CTLA-4, composed of aMYPPPY motif, with a surface on B7 formed predominately by the G, F, C,C′ and C″ strands (Schwartz, et al., (2001) supra; and Stamper, et al.,(2001) supra.). Data from ammo acid homologies, mutation, and computermodeling provide support for the concept that this motif also is a majorB7-binding site for CD28 (Bajorath, et al., J. Mol. Graph. Model.,15:135-139 (1997)). Although the MYPPPY motif is not conserved in ICOS,studies have indicated that a related motif having the sequence FDPPPFand located at the analogous position is a major determinant for bindingof ICOS to B7-H2 (Wand, et al., J. Exp. Med., 195:1033-1041 (2002)).

B7-DC (also called PD-L2) is a relatively new member of the B7 family,and has an amino acid sequence that is about 34% identical to B7-H1(also called PD-L1). Human and mouse B7-DC orthologues share about 70%amino acid identity. While B7-H1 and B7-DC transcripts are found invarious tissues (Dong, et al. (1999) supra; Latchman, et al. (2001)supra; and Tamura, Blood, 97:1809-1816 (2001)), the expression profilesof the proteins are quite distinct. Expression of B7-H1 protein,although essentially not found in normal tissues other thanmacrophage-like cells, can be induced in a variety of tissues and celltypes (Dong, et al. (1999) supra; Tamura, et al. (2001) supra; andIshida, et al., Immunol. Lett., 84:57-62 (2000)). In contrast, B7-DC isexpressed only in dendritic cells and monocytes (Tseng, et al. (2001)supra; and Ishida, et al. (2000) supra).

It has been shown that both B7-H1 and B7-DC bind to PD-1 (programmedcell death-1) (Freeman, et al., J. Exp. Med., 192:1027-1034 (2000);Tseng (2001) supra; Latchman (2001) supra), a distant member of the CD28family with an immunoreceptor tyrosine-based inhibitory motif (ITIM) inits cytoplasmic domain (Ishida, et al., EMBO J., 11:3887-3895 (1992)).PD-1 is expressed on a subset of thymocytes and up-regulated on T, B,and myeloid cells after activation (Agata, et al., Int. Immunol.,8:765-772 (1996)). The phenotypes of PD-1^(−/−) mice provide directevidence for PD-1 being a negative regulator of immune responses invivo. In the absence of PD-1, mice on the C57BL/6 background slowlydevelop a lupus-like glomerulonephritis and progressive arthritis(Nishimura, et al., Immunity, 11:141-151 (1999)). PD-1^(−/−) mice on theBALB/c background rapidly develop a fatal autoimmune dilatedcardiomyopathy (Nishimura, et al., Science. 291:319-322 (2001)).However, substantial evidence indicates that B7-DC can function tocostimulate T cell responses. In the presence of suboptimal TCR signals,B7-DC stimulates increased proliferation and production of cytokines invitro (Tseng, et al., J. Exp. Med. 193:839-846 (2001)). On the otherhand, in vitro studies indicate a negative regulatory role for B7-DC inT cell responses (Latchman (2001) supra). These seemingly contradictorydata are best interpreted by expression of additional receptors forB7-DC on T cells other than PD-1.

It would be advantageous to provide compositions that increaseantigen-specific proliferation of T cells, enhance production ofcytokines, stimulate differentiation and effector function, and promotesurvival of T cells. It would also be advantageous to provide B7-DCvariant polypeptides that have reduced binding affinity for PD-1compared to wild type B7-DC, yet retain the ability to costimulate Tcells (i.e., increase antigen-specific proliferation of T cells, enhancecytokine production by T cells, stimulate differentiation and effectorfunctions of T cells, or promote survival of T cells).

It is therefore an object of the present invention to provide B7-DCvariant polypeptides that have reduced binding affinity for PD-1compared to wild type B7-DC, yet retain the ability to costimulate Tcells.

It is another object of the present invention to provide isolatednucleic acid molecules encoding variant B7-DC polypeptides.

It is another object of the present invention to provide cellscontaining vectors that express nucleic acid molecules encoding variantB7-DC polypeptides.

It is a still further an object of the present invention to providemethods for costimulating T cells by contacting them with variant B7-DCpolypeptides.

It is still a further object of the invention to provide methods foradministering variant B7-DC polypeptides, nucleic acids encoding thesame, or cells transfected or transduced with nucleic acids encodingvariant B7-DC polypeptides to a mammal in need thereof.

It is still a further object of the invention to provide methods forpotentiating an immune response to an antigen or a vaccine byadministering variant B7-DC polypeptides in combination with the antigenor vaccine.

SUMMARY OF THE INVENTION

Compositions and methods for costimulating T cells (i.e., increasingantigen-specific proliferation of T cells, enhancing cytokine productionby T cells, stimulating differentiation ad effector functions of T cellsand/or promoting T cell survival) are provided. Suitable compositionsinclude variant B7-DC polypeptides. Variant B7-DC polypeptides havereduced binding affinity for the inhibitory PD-1 ligand andsubstantially retain the ability to costimulate T cells. In certainembodiments, variant B7-DC polypeptides can contain, without limitation,substitutions, deletions or insertions at position 33 of the A′β-strand, positions 39 or 41 of the B β-strand, positions 56 or 58 ofthe C β-strand, positions 65 or 67 of the C′ β-strand, positions 71 or72 of the C″ β-strand, position 84 of the D β-strand, position 88 of theE β-strand, positions 101, 103 or 105 of the F β-strand, or positions111, 113 or 116 of the G β-strand of murine or human B7-DC.

Fragments of variant B7-DC polypeptides and fusion proteins containingvariant B7-DC polypeptides are also provided. In some embodiments,fragments of variant B7-DC polypeptides include soluble fragments,including the extracellular domain or a fragment thereof. Other suitablefragments of variant B7-DC polypeptides include fragments containing theIgV and IgC domains or fragments containing only the IgV domain. VariantB7-DC polyeptides and fragments thereof can be coupled to otherpolypeptides to form fusion proteins. Provided are variant B7-DC fusionpolypeptides having a first fusion partner comprising all or a part of avariant B7-DC protein fused (i) directly to a second polypeptide or,(ii) optionally, fused to a linker peptide sequence that is fused to thesecond polypeptide. The presence of the fusion partner can alter thesolubility, affinity and/or valency of the variant B7-DC polypeptide. Incertain embodiments, variants B7-DC polypeptides are fused to one ormore domains of an Ig heavy chain constant region, preferably having anamino acid sequence corresponding to the hinge, C_(H2) and C_(H3)regions of a human immunoglobulin Cγ1 chain.

Nucleic acids encoding variant B7-DC polypeptides and variant B7-DCfusion proteins and host cells containing such nucleic acids in vectorsare also provided.

Immunogenic compositions containing variant B7-DC polypeptides andvariant B7-DC fusion proteins are also provided. Immunogeniccompositions include antigens, a source of variant B7-DC polypeptidesand optionally adjuvants and targeting molecules. Suitable antigensinclude viral, bacterial, parasite, environmental and tumor antigens.

Methods for using variant B7-DC polypeptides and variant B7-DC fusionproteins to costimulate T cells are provided. T cells can becostimulated with variant B7-DC compositions in vitro, ex vivo or invivo. Costimulation of T cells using variant B7-DC compositions canoccur before, during or after antigen-specific activation of the T cell.

Therapeutic uses of variant B7-DC polypeptides, variant B7-DC fusionproteins and nucleic acids encoding the same are provided. Variant B7-DCcompositions can be used to stimulate the immune response to cancer andinfectious diseases, including viral infections. Variant B7-DCcompositions can also be used to stimulate the immune response ofimmunosuppressed subjects. In certain embodiments, variant B7-DCcompositions are administered in conjunction with vaccines.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of the full-length, immature amino acid sequenceof human B7-DC (hB7-DC) (SEQ ID NO: 1). The signal sequence of humanB7-DC contains the first 19 amino acids of the full-length immatureamino acid sequence.

FIG. 2 is a depiction of the full-length, immature amino acid sequenceof mouse B7-DC (mB7-DC) (SEQ ID NO: 2). The signal sequence of murineB7-DC contains the first 19 amino acids of the full-length immatureamino acid sequence.

FIG. 3 is a depiction of a nucleotide sequence (SEQ ID NO: 3) encoding afull-length, immature human B7-DC polypeptide (SEQ ID NO: 1) having theamino acid sequence shown in FIG. 1. The signal sequence of human B7-DCis encoded by the first 57 nucleotides of the full-length immaturenucleic acid sequence.

FIG. 4 is a depiction of a nucleotide sequence (SEQ ID NO: 4) encoding afull-length, immature mouse B7-DC polypeptide (SEQ ID NO: 2) having theamino acid sequence shown in FIG. 2. The signal sequence of murine B7-DCis encoded by the first 57 nucleotides of the full-length immaturenucleic acid sequence.

FIG. 5 is a structure-oriented sequence alignment of mouse and human B7molecules. The alignment includes sequences from the N-terminal IgVdomains of human CD86 (hCD86) (SEQ ID NO: 5), human CD80 (hCD80) (SEQ IDNO: 6), human B7-H1 (hB7-H1) (SEQ ID NO: 7), mouse B7-H1 (mB7-H1) (SEQID NO: 8), human B7-H2 (hB7-H2) (SEQ ID NO: 9), human B7-H3 (hB7-H3)(SEQ ID NO: 10), human B7-DC (hPD-L2) (SEQ ID NO: 1), and mouse B7-DC(mPD-L2) (SEQ ID NO: 12). β-strands observed in the x-ray structures ofCDS0 and CD86 are labeled (A′-G), and residue positions most conservedacross the B7 family (e.g., large hydrophobic, charged/polar, orcysteine residues) are not bolded. Potential N-linked glycosylationsites are boxed. CD86 residues that are underlined are involved information of the crystallographic homodimer interface, which isconserved in CD80, and residues shown in bold and underlined fontparticipate in CTLA-4 binding in the structure of the complex. Residuepositions in mB7-H1 and mB7-DC that are most important for PD-1 binding,based on mutagenesis studies, are in bold type. Residues in mB7-H1 that,when mutagenized, demonstrated increased avidity for PD-1 are circled.Residue numbers indicate positions within mB7-H1 (upper numbers) andmB7-DC (lower numbers).

FIG. 6 is a line graph showing results from surface plasmon resonanceanalysis of B7-DC binding to PD-1. The graph shows results for bindingof wild type B7-DCIg and K113S B7-DCIg variant to immobilized PD-1Ig.Data are reported in terms of response units (RU) as a function of timein seconds.

FIG. 7 is a series of graphs showing the binding of wild type andvariant B7-DCIg fusion proteins to CHO cells expressing PD-1. TheB7-DCIg fusion proteins were incubated with the indicated wild type orvariant B7-DC variant fusion protein and then with a FITC-labeled goatanti-human IgG and analyzed by FACS. Media alone and human IgG were usedas negative controls and anti-human PD-1 antibody was used as a positivecontrol. The graphs represent the number of cells as a function of levelof emitted fluorescence. The numbers on the right and left sides of thegraphs represent the percentage of cells that were considered to bepositive and negative, respectively, for binding of the indicatedcomposition.

FIGS. 8A and 8B are graphs showing effects of wild type and variantB7-DC molecules on T-cell costimulation. Data in FIG. 8A represent Tcell proliferation after stimulation with the indicated wild type (-⋄-)or variant (-▪-D111; -x-K113) B7-DC Ig fusion proteins in the presenceof anti-CD3 mAb coated onto the well-bottoms of 96-well plates at theindicated concentrations. T cell proliferation was measured asincorporation of ³H-Thymidine (³H-TdR) (×10³ cpm) as a function of theconcentration of anti-CD3 mAb (μg/ml). Human Ig (hlg) (-∘-) and PBSalone (-▴-) were used as negative controls for the costimulatorymolecules. Data depict one representative experiment of three. Data inFIG. 8B represent IFN-γ secretion (ng/ml) by T cells cultured in thepresence of the indicated Ig fusion proteins and anti-CD3 for 48 or 72hours. Human Ig and PBS were used as negative controls. Data depict onerepresentative experiment of three.

FIG. 9 is a line graph showing proliferation of PD-1^(−/−) T cells afterincubation with the indicated wild type (-●-) or variant (-Δ-D111;-x-K113) B7-DC Ig fusion proteins in the presence of anti-CD3 mAb. Tcell proliferation was measured as incorporation of ³H-Thymidine(³H-TdR) (×10³ cpm) as a function of the concentration of anti-CD3 mAb(μg/ml). Human Ig (-▪-) and PBS (-∘-) were used as negative controls.Data depict one representative experiment of three.

FIG. 10 is a line graph showing growth (mean tumor diameter inmillimeters) of EG7 murine tumor cells that were either mock transfected(-□-) or transfected with wild-type B7-DC (-▪-) or K113S B7-DC (-●-) insyngeneic immunocompetent (C57BL/6) mice as a function of time (days).

FIG. 11 is a line graph showing growth (mean tumor diameter inmillimeters) of EG7 murine tumor cells that were either mock transfected(-□-) or transfected with wild-type B7-DC (-▪-) or K113S B7-DC (-●-) inimmunodeficient nude (nu/nu) mice as a function of time (days).

FIG. 12 is a line graph showing growth (mean tumor diameter inmillimeters) of P815 mastrocytoma murine tumor cells that were eithermock transfected (-□-) or transfected with wild-type B7-DC (-▪-) orK113S B7-DC (-●-) in syngeneic immunocompetent (DBA/2) mice as afunction of time (days).

FIG. 13 is a line graph showing growth (mean tumor diameter inmillimeters) of P815 mastrocytoma murine tumor cells that were eithermock transfected (-□-) or transfected with wild-type B7-DC (-▪-) orK113S B7-DC (-●-) in immunodeficient nude (nu/nu) mice as a function oftime (days).

FIG. 14 is a line graph showing showing the effect of intraperitonealinjection of wild-type B7-DCIg on growth (mean tumor diameter inmillimeters) of P815 mastrocytoma murine tumor cells in syngeneicimmunocompetent (DBA/2) mice as a function of time (days). Mice wereinjected intraperitonealy with 0.1 mg of control Ig (-□-) or wild-typeB7-DCIg (-▪-) on day 3 and day 8.

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

As used herein the term “isolated” is meant to describe a compound ofinterest (e.g., either a polynucleotide or a polypeptide) that is in anenvironment different from that in which the compound naturally occurse.g. separated from its natural milieu such as by concentrating apeptide to a concentration at which it is not found in nature.“Isolated” is meant to include compounds that are within samples thatare substantially enriched for the compound of interest and/or in whichthe compound of interest is partially or substantially purified.

As used herein, the term “polypeptide” refers to a chain of amino acidsof any length, regardless of modification (e.g., phosphorylation orglycosylation).

As used herein, a “costimulatory polypeptide” is a polypeptide that,upon interaction with a cell-surface molecule on T cells, enhances Tcell responses, enhances proliferation of T cells, enhances productionand/or secretion of cytokines by T cells, stimulates differentiation andeffector functions of T cells or promotes survival of T cells relativeto T cells not contacted with a costimulatory peptide.

As used herein, a “variant” polypeptide contains at least one amino acidsequence alteration as compared to the amino acid sequence of thecorresponding wild-type polypeptide.

As used herein, an “amino acid sequence alteration” can be, for example,a substitution, a deletion, or an insertion of one or more amino acids.

As used herein, a “vector” is a replicon, such as a plasmid, phage, orcosmid, into which another DNA segment may be inserted so as to bringabout the replication of the inserted segment. The vectors describedherein can be expression vectors.

As used herein, an “expression vector” is a vector that includes one ormore expression control sequences

As used herein, an “expression control sequence” is a DNA sequence thatcontrols and regulates the transcription and/or translation of anotherDNA sequence.

As used herein, “operably linked” means incorporated into a geneticconstruct so that expression control sequences effectively controlexpression of a coding sequence of interest.

As used herein, a “fragment” of a polypeptide refers to any subset ofthe polypeptide that is a shorter polypeptide of the full lengthprotein. Generally, fragments will be five or more amino acids inlength.

As used herein, “valency” refers to the number of binding sitesavailable per molecule.

As used herein, “conservative” amino acid substitutions aresubstitutions wherein the substituted amino acid has similar structuralor chemical properties.

As used herein, “non-conservative” amino acid substitutions are those inwhich the charge, hydrophobicity, or bulk of the substituted amino acidis significantly altered.

As used herein, “isolated nucleic acid” refers to a nucleic acid that isseparated from other nucleic acid molecules that are present in amammalian genome, including nucleic acids that normally flank one orboth sides of the nucleic acid in a mammalian genome (e.g., nucleicacids that encode non-B7-DC proteins).

As used herein with respect to nucleic acids, the term “isolated”includes any non-naturally-occurring nucleic acid sequence, since suchnon-naturally-occurring sequences are not found in nature and do nothave immediately contiguous sequences in a naturally-occurring genome.

As used herein, the term “host cell” refers to prokaryotic andeukaryotic cells into which a recombinant expression vector can beintroduced.

As used herein, “transformed” and “transfected” encompass theintroduction of a nucleic acid (e.g. a vector) into a cell by a numberof techniques known in the art.

As used herein, the term “antibody” is meant to include both intactmolecules as well as fragments thereof that include the antigen-bindingsite. These include Fab and F(ab′)₂ fragments which lack the Fc fragmentof an intact antibody.

The terms “individual”, “host”, “subject”, and “patient” are usedinterchangeably herein, and refer to a mammal, including, but notlimited to, murines, simians, humans, mammalian farm animals, mammaliansport animals, and mammalian pets.

As used herein the term “effective amount” or “therapeutically effectiveamount” means a dosage sufficient to treat, inhibit, or alleviate one ormore symptoms of an inflammatory response or autoimmune disease statebeing treated or to otherwise provide a desired pharmacologic and/orphysiologic effect. The precise dosage will vary according to a varietyof factors such as subject-dependent variables (e.g., age, immune systemhealth, etc.), the disease, and the treatment being effected.

II. Compositions

A. Isolated B7-DC Polypeptides

1. Variant B7-DC Polypeptides

Isolated B7-DC polypeptides are disclosed herein. The B7-DC polypeptidemay be of any species of origin. In one embodiment, the B7-DCpolypeptide is from a mammalian species. In a preferred embodiment, theB7-DC polypeptide is of murine or human origin. The full-length,immature amino acid sequence of mouse B7-DC (SEQ ID NO: 2) is depictedin FIG. 2. The signal sequence of murine B7-DC contains the first 19amino acids of the full-length immature amino acid sequence. Thefull-length, immature amino acid sequence of human B7-DC (SEQ ID NO: 1)is depicted in FIG. 1. The signal sequence of human B7-DC contains thefirst 19 amino acids of the full-length immature amino acid sequence. Asused herein, the term “polypeptide” refers to a chain of amino acids ofany length, regardless of modification (e.g., phosphorylation orglycosylation).

In one embodiment the variant B7-DC polypeptide has the same activity,substantially the same activity, or different activity as wildtypeB7-DC. Substantially the same activity means it retains the ability toco-stimulate T cells.

The polypeptides disclosed herein include variant B7-DC polypeptides. Asused herein, a “variant” polypeptide contains at least one amino acidsequence alteration as compared to the amino acid sequence of thecorresponding wild-type polypeptide. An amino acid sequence alterationcan be, for example, a substitution, a deletion, or an insertion of oneor more amino acids.

A variant B7-DC polypeptide can have any combination of amino acidsubstitutions, deletions or insertions. In one embodiment, isolatedB7-DC variant polypeptides have an integer number of amino acidalterations such that their amino acid sequence shares at least 60, 70,80, 85, 90, 95, 97, 98, 99, 99.5 or 100% identity with an amino acidsequence of a wild type B7-DC polypeptide. In a preferred embodiment,B7-DC variant polypeptides have an amino acid sequence sharing at least60, 70, 80, 85, 90, 95, 97, 98, 99, 99.5 or 100% identity with the aminoacid sequence of a wild type murine or wild type human B7-DCpolypeptide.

Percent sequence identity can be calculated using computer programs ordirect sequence comparison. Preferred computer program methods todetermine identity between two sequences include, but are not limitedto, the GCG program package, FASTA, BLASTP, and TBLASTN (see, e.g., D.W. Mount, 2001, Bioinformatics: Sequence and Genome Analysis, ColdSpring Harbor Laboratory Press, Cold Spring Harbor, N.Y.). The BLASTPand TBLASTN programs are publicly available from NCBI and other sources.The well-known Smith Waterman algorithm may also be used to determineidentity.

Exemplary parameters for amino acid sequence comparison include thefollowing: 1) algorithm from Needleman and Wunsch (J. Mol. Biol.,48:443-453 (1970)); 2) BLOSSUM62 comparison matrix from Hentikoff andHentikoff (Proc. Natl. Acad. Sci. U.S.A., 89:10915-10919 (1992)) 3) gappenalty=12; and 4) gap length penalty=4. A program useful with theseparameters is publicly available as the “gap” program (Genetics ComputerGroup, Madison, Wis.). The aforementioned parameters are the defaultparameters for polypeptide comparisons (with no penalty for end gaps).

Alternatively, polypeptide sequence identity can be calculated using thefollowing equation: % identity=(the number of identicalresidues)/(alignment length in amino acid residues)*100. For thiscalculation, alignment length includes internal gaps but does notinclude terminal gaps.

Amino acid substitutions in B7-DC polypeptides may be “conservative” or“non-conservative”. As used herein, “conservative” amino acidsubstitutions are substitutions wherein the substituted amino acid hassimilar structural or chemical properties, and “non-conservative” aminoacid substitutions are those in which the charge, hydrophobicity, orbulk of the substituted amino acid is significantly altered.Non-conservative substitutions will differ more significantly in theireffect on maintaining (a) the structure of the peptide backbone in thearea of the substitution, for example, as a sheet or helicalconformation, (b) the charge or hydrophobicity of the molecule at thetarget site, or (c) the bulk of the side chain.

Examples of conservative amino acid substitutions include those in whichthe substitution is within one of the five following groups: 1) smallaliphatic, nonpolar or slightly polar residues (Ala, Ser, Thr, Pro,Gly); 2) polar, negatively charged residues and their amides (Asp, Asn,Glut, Gln); polar, positively charged residues (His, Arg, Lys); largealiphatic, nonpolar residues (Met, Leu, Ile, Val, Cys); and largearomatic resides (Phe, Tyr, Trp). Examples of non-conservative aminoacid substitutions are those where 1) a hydrophilic residue, e.g., serylor threonyl, is substituted for (or by) a hydrophobic residue, e.g.,leucyl, isoleucyl, phenylalanyl, valyl, or alanyl; 2) a cysteine orproline is substituted for (or by) any other residue; 3) a residuehaving an electropositive side chain, e.g., lysyl, arginyl, or histidyl,is substituted for (or by) an electronegative residue, e.g., glutamyl oraspartyl; or 4) a residue having a bulky side chain, e.g.,phenylalanine, is substituted for (or by) a residue that does not have aside chain, e.g., glycine.

B7 family molecules, including B7-DC are expressed at the cell surfaceas homodimers with a membrane proximal constant IgC domain and amembrane distal IgV domain. Receptors for these ligands share a commonextracellular IgV-like domain. Interactions of receptor-ligand pairs aremediated predominantly through residues in the IgV domains of theligands and receptors. In general, IgV domains are described as havingtwo sheets that each contain a layer of β-strands. These β-strands arereferred to as A′, B, C, C′, C″, D, E, F and G. In one embodiment theB7-DC variant polypeptides contain amino acid alterations (i.e.,substitutions, deletions or insertions) within one or more of theseβ-strands in any possible combination. In another embodiment, B7-DCvariants contain one or more amino acid alterations (i.e.,substitutions, deletions or insertions) within the A′, C, C′, C″, D, E,F or G β-strands. In a preferred embodiment B7-DC variants contain oneor more amino acid alterations in the G β-strand.

With respect to murine B7-DC or human B7-DC, a variant B7-DC polypeptidecan contain, without limitation, substitutions, deletions or insertionsat position 33 of the A′ β-strand, positions 39 or 41 of the B β-strand,positions 56 or 58 of the C β-strand, positions 65 or 67 of the C′β-strand, positions 71 or 72 of the C″ β-strand, position 84 of the Dβ-strand, position 88 of the E β-strand, positions 101, 103 or 105 ofthe F β-strand, or positions 111, 113 or 116 of the G β-strand.

In one embodiment, variant B7-DC polypeptides contain a substitution atposition 33 (e.g., a serine substitution for aspartic acid at position33), a substitution at position 39 (e.g., a tyrosine substitution forserine at position 39), a substitution at position 41 (e.g., a serinesubstitution for glutamic acid at position 41), a substitution atposition 56 (e.g., a serine substitution for arginine at position 56), asubstitution at position 58 (e.g., a tyrosine substitution for serine atposition 58), a substitution at position 65 (e.g., a serine substitutionfor aspartic acid at position 65), a substitution at position 67 (e.g.,a tyrosine substitution for serine at position 67), a substitution atposition 71 (e.g., a serine substitution for glutamic acid at position71), a substitution at position 72 (e.g., a serine substitution forarginine at position 72), a substitution at position 84 (e.g., a serinesubstitution for lysine at position 84), a substitution at position 88(e.g., an alanine substitution for histidine at position 88), asubstitution at position 101 (e.g., a serine substitution for arginineat position 101), a substitution at position 103 (e.g., an alaninesubstitution for leucine at position 103), a substitution at position105 (e.g., an alanine substitution for isoleucine at position 105), asubstitution at position 111 (e.g., a serine substitution for asparticacid at position 111), a substitution at position 113 (e.g., a serinesubstitution for lysine at position 113), or a substitution at position116 (e.g., a tyrosine substitution for threonine at position 116).

It is understood, however, that substitutions at the recited amino acidpositions can be made using any amino acid or amino acid analog. Forexample, the substitutions at the recited positions can be made with anyof the naturally occurring amino acids (e.g., alanine, aspartic acid,asparagine, arginine, cysteine, glycine, glutamic acid, glutamine,histidine, leucine, valine, isoleucine, lysine, methionine, proline,threonine, serine, phenylalanine, tryptophan, or tyrosine).

While the substitutions described herein are with respect to mouse andhuman B7-DC, it is noted that one of ordinary skill in the art couldreadily make equivalent alterations in the corresponding polypeptidesfrom other species (e.g., rat, hamster, guinea pig, gerbil, rabbit, dog,cat, horse, pig, sheep, cow or non-human primate).

2. Properties of Variant B7-DC Polypeptides

The disclosed isolated B7-DC polypeptides are capable of costimulating Tcells. A “costimulatory polypeptide” is a polypeptide that, uponinteraction with a cell-surface molecule on a T cell, enhances T cellresponses, enhances proliferation of T cells, enhances production and/orsecretion of cytokines by T cells, stimulates differentiation andeffector functions of T cells or promotes survival of T cells relativeto T cells not contacted with a costimulatory peptide. The T cellresponse that results from the interaction typically is greater than theresponse in the absence of the costimulatory polypeptide. The responseof the T cell in the absence of the costimulatory polypeptide can be noresponse or can be a response significantly lower than in the presenceof the costimulatory polypeptide. The response of the T cell can be aneffector (e.g., CTL or antibody-producing B cell) response, a helperresponse providing help for one or more effector (e.g., CTL orantibody-producing B cell) responses, or a suppressive response.

Variant B7-DC polypeptides disclosed herein have reduced bindingaffinity for PD-1 as compared to the binding affinity of thecorresponding wild-type B7-DC polypeptide. The binding affinity of avariant typically is reduced by at least 50 percent, 55 percent, 60percent, 70 percent, 75 percent, 80 percent, 90 percent, 95 percent, 99percent, or more than 99 percent as compared to the binding affinity ofthe corresponding wild-type polypeptide.

Methods for measuring the binding affinity between two molecules arewell known in the art. Methods for measuring the binding affinity ofB7-DC variant polypeptides for PD-1 include, but are not limited to,fluorescence activated cell sorting (FACS), surface plasmon resonance,fluorescence anisotropy, affinity chromatography and affinityselection-mass spectrometry.

In addition, disclosed variant B7-DC polypeptides with reduced bindingaffinity for PD-1 retain substantial costimulatory activity. Forexample, a variant B7-DC polypeptide can have at least 20 percent, 25percent, 30 percent, 40 percent, 50 percent, 60 percent, 75 percent, 90percent, 100 percent, or more than 100 percent of the level ofcostimulatory activity exhibited by the corresponding wild-type B7-DCpolypeptide.

Methods for measuring costimulation of T cells are well known in the artand include measurements of T cell proliferation and secretion ofcytokines, including, but not limited to, Il-2, IL-4, IL-5, IL-6, IL-10,IL-13, and IFN-γ. Proliferation of T cells can be measured by a numberof methods including, but not limited to, cell counting, measuring DNAsynthesis by uptake of labeled nucleotides (such as [³H] TdR and BrdU)and measuring metabolic activity with tetrazolium salts. Methods formeasuring the secretion of cytokines include, but are not limited to,ELISA.

3. Fragments of Variant B7-DC Polypeptides

The B7-DC polypeptides disclosed herein can be full-length polypeptides,or can be a fragment of a full length B7-DC polypeptide. As used herein,a fragment of B7-DC refers to any subset of the polypeptide that is ashorter polypeptide of the full length protein.

In one embodiment, variant B7-DC polypeptide fragments are those thatretain the ability to costimulate T cells. A variant B7-DC polypeptidethat is a fragment of full-length B7-DC typically has at least 20percent, 30 percent, 40 percent, 50 percent, 60 percent, 70 percent, 80percent, 90 percent, 95 percent, 98 percent, 99 percent, 100 percent, oreven more than 100 percent of the costimulatory activity of thefull-length variant B7-DC polypeptide.

Human and mouse B7-DC proteins contain a short intracytoplasmic domain,a single transmembrane domain and an extracellular domain. Theextracellular domain contains two Ig domains; a membrane proximal IgCdomain and a membrane distal IgV domain. Useful fragments of variantB7-DC polypeptides include soluble fragments. Soluble B7-DC fragmentsare fragments of B7-DC that may be shed, secreted or otherwise extractedfrom the producing cells. In one embodiment, variant B7-DC polypeptidefragments include the entire extracellular domain of B7-DC. Theextracellular domain of B7-DC includes amino acids from about 26 toabout amino acid 226 of murine or human B7-DC or costimulatory fragmentsthereof. In another embodiment, variant B7-DC polypeptide fragmentsinclude the IgC and IgV domains of B7-DC. In another embodiment, variantB7-DC polypeptide fragments include the IgV domain of B7-DC.

In one embodiment, variant B7-DC polypeptide fragments may contain aregion of the polypeptide that is important for binding affinity forPD-1. These polypeptide fragments may be useful to compete for bindingto PD-1 and to prevent native B7-DC from binding to PD-1. By competingfor binding to PD-1, these fragments may be useful to enhance an immuneresponse, as inhibiting interactions of B7-H1 and B7-DC with PD-1 mayalso inhibit the suppression of immune responses that would otherwiseoccur. A polypeptide fragment of mouse or human B7-DC that couldcompetitively bind to PD-1 can contain, for example, amino acids 67-71,101-105, or 111-113. The binding of B7-DC to PD-1 typically is inhibitedby at least 50 percent, 60 percent, 70 percent, 75 percent, 80 percent,90 percent, 95 percent, or more than 95 percent as compared to the levelof binding of B7-DC to PD-1 in the absence of the fragment.

4. Modified Variant B7-DC Polypeptides

Variant B7-DC polypeptides may be modified by chemical moieties that maybe present in polypeptides in a normal cellular environment, forexample, phosphorylation, methylation, amidation, sulfation, acylation,glycosylation, sumoylation and ubiquitylation. Variant B7-DCpolypeptides may also be modified with a label capable of providing adetectable signal, either directly or indirectly, including, but notlimited to, radioisotopes and fluorescent compounds.

Variant B7-DC polypeptides may also be modified by chemical moietiesthat are not normally added to polypeptides in a cellular environment.Such modifications may be introduced into the molecule by reactingtargeted amino acid residues of the polypeptide with an organicderivatizing agent that is capable of reacting with selected side chainsor terminal residues. Another modification is cyclization of theprotein.

Examples of chemical derivatives of the polypeptides include lysinyl andamino terminal residues derivatized with succinic or other carboxylicacid anhydrides. Derivatization with a cyclic carboxylic anhydride hasthe effect of reversing the charge of the lysinyl residues. Othersuitable reagents for derivatizing amino-containing residues includeimidoesters such as methyl picolinimidate; pyridoxal phosphate;pyridoxal; chloroborohydride; trinitrobenzenesulfonic acid;O-methylisourea; 2,4 pentanedione; and transaminase-catalyzed reactionwith glyoxylate. Carboxyl side groups, aspartyl or glutamyl, may beselectively modified by reaction with carbodiimides (R—N═C═N—R′) such as1-cyclohexyl-3-(2-morpholinyl-(4-ethyl)carbodiimide or1-ethyl-3-(4-azonia-4,4-dimethylpentyl) carbodiimide. Furthermore,aspartyl and glutamyl residues can be converted to asparaginyl andglutaminyl residues by reaction with ammonia. Polypeptides may alsoinclude one or more D-amino acids that are substituted for one or moreL-amino acids.

5. Variant B7-DC Fusion Polypeptides

The variant B7-DC polypeptides disclosed herein may be coupled to otherpolypeptides to form fusion proteins. Provided are variant B7-DC fusionpolypeptides having a first fusion partner comprising all or a part of avariant B7-DC protein fused (i) directly to a second polypeptide or,(ii) optionally, fused to a linker peptide sequence that is fused to thesecond polypeptide. The presence of the fusion partner can alter thesolubility, affinity and/or valency of the variant B7-DC polypeptide. Asused herein, “valency” refers to the number of binding sites availableper molecule. Variant B7-DC fusion proteins described herein include anycombination of amino acid alteration (i.e. substitution, deletion orinsertion), fragment of B7-DC, and/or modification as described above.In one embodiment, variant B7-DC fusion proteins include theextracellular domain of a B7-DC protein, or a costimulatory fragmentthereof; as the first binding partner. In another embodiment, variantB7-DC fusion proteins include the IgV and IgC domain of a B7-DC proteinas the first binding partner. In another embodiment, variant B7-DCfusion proteins include the IgV domain of a B7-DC protein as the firstbinding partner.

The second polypeptide binding partner may be N-terminal or C-terminalrelative to the variant B7-DC polypeptide. In a preferred embodiment,the second polypeptide is C-terminal to the variant B7-DC polypeptide.

A large number of polypeptide sequences that are routinely used asfusion protein binding partners are well known in the art. Examples ofuseful polypeptide binding partners include, but are not limited to,green fluorescent protein (GFP), glutathione S-transferase (GST),polyhistidine, myc, hemaglutinin, Flag™ tag (Kodak, New Haven, Conn.),maltose E binding protein and protein A. In one embodiment, the variantB7-DC fusion protein is fused to one or more domains of an Ig heavychain constant region, preferably having an amino acid sequencecorresponding to the hinge, C_(H2) and C_(H3) regions of a humanimmunoglobulin Cγ1 chain.

B. Isolated Nucleic Acid Molecules

Isolated nucleic acid sequences encoding variant B7-DC polypeptides aredisclosed herein. As used herein, “isolated nucleic acid” refers to anucleic acid that is separated from other nucleic acid molecules thatare present in a mammalian genome, including nucleic acids that normallyflank one or both sides of the nucleic acid in a mammalian genome (e.g.,nucleic acids that encode non-B7-DC proteins). The term “isolated” asused herein with respect to nucleic acids also includes anynon-naturally-occurring nucleic acid sequence, since suchnon-naturally-occurring sequences are not found in nature and do nothave immediately contiguous sequences in a naturally-occurring genome.

An isolated nucleic acid can be, for example, a DNA molecule, providedone of the nucleic acid sequences normally found immediately flankingthat DNA molecule in a naturally-occurring genome is removed or absent.Thus, an isolated nucleic acid includes, without limitation, a DNAmolecule that exists as a separate molecule independent of othersequences (e.g., a chemically synthesized nucleic acid, or a cDNA orgenomic DNA fragment produced by PCR or restriction endonucleasetreatment), as well as recombinant DNA that is incorporated into avector, an autonomously replicating plasmid, a virus (e.g., aretrovirus, lentivirus, adenovirus, or herpes virus), or into thegenomic DNA of a prokaryote or eukaryote. In addition, an isolatednucleic acid can include an engineered nucleic acid such as arecombinant DNA molecule that is part of a hybrid or fusion nucleicacid. A nucleic acid existing among hundreds to millions of othernucleic acids within, for example, a cDNA library or a genomic library,or a gel slice containing a genomic DNA restriction digest, is not to beconsidered an isolated nucleic acid.

Nucleic acids can be in sense or antisense orientation, or can becomplementary to a reference sequence encoding a B7-DC polypeptide.Reference sequences include, for example, the nucleotide sequence ofhuman B7-DC (SEQ ID NO: 3) set forth in FIG. 3, which encodesfull-length, immature B7-DC having the amino acid sequence (SEQ IDNO: 1) set forth in FIG. 1 and the nucleotide sequence of murine B7-DC(SEQ ID NO: 4) set forth in FIG. 4, which encodes full-length, immatureB7-DC having the amino acid sequence (SEQ ID NO: 2) set forth in FIG. 2.

Nucleic acids can be DNA, RNA, or nucleic acid analogs. Nucleic acidanalogs can be modified at the base moiety, sugar moiety, or phosphatebackbone. Such modification can improve, for example, stability,hybridization, or solubility of the nucleic acid. Modifications at thebase moiety can include deoxyuridine for deoxythymidine, and5-methyl-2′-deoxycytidine or 5-bromo-2′-deoxycytidine for deoxycytidine.Modifications of the sugar moiety can include modification of the 2′hydroxyl of the ribose sugar to form 2′-O-methyl or 2′-O-allyl sugars.The deoxyribose phosphate backbone can be modified to produce morpholinonucleic acids, in which each base moiety is linked to a six membered,morpholino ring, or peptide nucleic acids, in which the deoxyphosphatebackbone is replaced by a pseudopeptide backbone and the four bases areretained. See, for example, Summerton and Weller (1997) AntisenseNucleic Acid Drug Dev. 7:187-195; and Hyrup et al. (1996) Bioorgan. Med.Chem. 4:5-23. In addition, the deoxyphosphate backbone can be replacedwith, for example, a phosphorothioate or phosphorodithioate backbone, aphosphoroamidite, or an alkyl phosphotriester backbone.

C. Vectors and Host Cells

Nucleic acids, such as those described above, can be inserted intovectors for expression in cells. As used herein, a “vector” is areplicon, such as a plasmid, phage, or cosmid, into which another DNAsegment may be inserted so as to bring about the replication of theinserted segment. Vectors can be expression vectors. An “expressionvector” is a vector that includes one or more expression controlsequences, and an “expression control sequence” is a DNA sequence thatcontrols and regulates the transcription and/or translation of anotherDNA sequence.

Nucleic acids in vectors can be operably linked to one or moreexpression control sequences. As used herein, “operably linked” meansincorporated into a genetic construct so that expression controlsequences effectively control expression of a coding sequence ofinterest. Examples of expression control sequences include promoters,enhancers, and transcription terminating regions. A promoter is anexpression control sequence composed of a region of a DNA molecule,typically within 100 nucleotides upstream of the point at whichtranscription starts (generally near the initiation site for RNApolymerase II). To bring a coding sequence under the control of apromoter, it is necessary to position the translation initiation site ofthe translational reading frame of the polypeptide between one and aboutfifty nucleotides downstream of the promoter. Enhancers provideexpression specificity in terms of time, location, and level. Unlikepromoters, enhancers can function when located at various distances fromthe transcription site. An enhancer also can be located downstream fromthe transcription initiation site. A coding sequence is “operablylinked” and “under the control” of expression control sequences in acell when RNA polymerase is able to transcribe the coding sequence intomRNA, which then can be translated into the protein encoded by thecoding sequence.

Suitable expression vectors include, without limitation, plasmids andviral vectors derived from, for example, bacteriophage, baculoviruses,tobacco mosaic virus, herpes viruses, cytomegalo virus, retroviruses,vaccinia viruses, adenoviruses, and adeno-associated viruses. Numerousvectors and expression systems are commercially available from suchcorporations as Novagen (Madison, Wis.), Clontech (Palo Alto, Calif.),Stratagene (La Jolla, Calif.), and Invitrogen Life Technologies(Carlsbad, Calif.).

An expression vector can include a tag sequence. Tag sequences, aretypically expressed as a fusion with the encoded polypeptide. Such tagscan be inserted anywhere within the polypeptide including at either thecarboxyl or amino terminus. Examples of useful tags include, but are notlimited to, green fluorescent protein (GFP), glutathione S-transferase(GST), polyhistidine, c-myc, hemagglutinin, Flag™ tag (Kodak, New Haven,Conn.), maltose E binding protein and protein A. In one embodiment, thevariant B7-DC fusion protein is present in a vector containing nucleicacids that encode one or more domains of an Ig heavy chain constantregion, preferably having an amino acid sequence corresponding to thehinge, C_(H2) and C_(H3) regions of a human immunoglobulin Cγ1 chain.

Vectors containing nucleic acids to be expressed can be transferred intohost cells. The term “host cell” is intended to include prokaryotic andeukaryotic cells into which a recombinant expression vector can beintroduced. As used herein, “transformed” and “transfected” encompassthe introduction of a nucleic acid molecule (e.g., a vector) into a cellby one of a number of techniques. Although not limited to a particulartechnique, a number of these techniques are well established within theart. Prokaryotic cells can be transformed with nucleic acids by, forexample, electroporation or calcium chloride mediated transformation.Nucleic acids can be transfected into mammalian cells by techniquesincluding, for example, calcium phosphate co-precipitation,DEAE-dextran-mediated transfection, lipofection, electroporation, ormicroinjection. Host cells (e.g., a prokaryotic cell or a eukaryoticcell such as a CHO cell) can be used to, for example, produce thevariant B7-DC polypeptides described herein. In some embodiments, a hostcell (e.g., an antigen presenting cell) can be used to express thevariant B7-DC polypeptides disclosed herein for presentation to a Tcell.

D). Antibodies

Monoclonal antibodies (mAbs) and methods for their production and useare described in Kohler and Milstein, Nature 256:495-497 (1975); U.S.Pat. No. 4,376,110; Hartlow, E. et al., Antibodies: A Laboratory Manual,Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1988);Monoclonal Antibodies and Hybridomas: A New Dimension in BiologicalAnalyses, Plenum Press, New York, N.Y. (1980); H. Zola et al., inMonoclonal Hybridoma Antibodies: Techniques and Applications, CRC Press,1982)).

Immunoassay methods are described in Coligan, J. E. et al., eds.,Current Protocols in Immunology, Wiley-Interscience, New York 1991 (orcurrent edition); Butt, W. R. (ed.) Practical Immunoassay: The State ofthe Art, Dekker, N.Y., 1984; Bizollon, Ch. A., ed., MonoclonalAntibodies and New Trends in Immunoassays, Elsevier, N.Y., 1984; Butler,J. E., ELISA (Chapter 29), In: van Oss, C. J. et al., (eds),IMMUNOCHEMISTRY, Marcel Dekker, Inc., New York, 1994, pp. 759-803;Butler, J. E. (ed.), Immunochemistry of Solid-Phase Immunoassay, CRCPress, Boca Raton, 1991; Weintraub, B., Principles of Radioimmunoassays,Seventh Training Course on Radioligand Assay Techniques, The EndocrineSociety, March, 1986; Work, T. S. et al., Laboratory Techniques andBiochemistry in Molecular Biology, North Holland Publishing Company, NY,(1978) (Chapter by Chard, T., “An Introduction to Radioimmune Assay andRelated Techniques”).

Anti-idiotypic antibodies are described, for example, in Idiotypy inBiology and Medicine, Academic Press, New York, 1984; ImmunologicalReviews Volume 79, 1984; Immunological Reviews Volume 90, 1986; Curr.Top. Microbiol, Immunol. Volume 119, 1985; Bona, C. et al., CRC Crit.Rev. Immunol., pp. 33-81 (1981); Jerme, N K, Ann. Immunol. 125C:373-389(1974); Jerne, N K, In: Idiotypes—Antigens on the Inside,Westen-Schnurr, I., ed., Editiones Roche, Basel, 1982, Urbain, J. etal., Ann. Immunol. 133D:179-(1982); Rajewsky, K. et al., Ann. Rev.Immunol. 1:569-607 (1983).

Monoclonal and polyclonal antibodies that are reactive with novelepitopes of B7-DC that are absent from known B7 family proteins aredescribed herein. The antibodies may be xenogeneic, allogeneic,syngeneic, or modified forms thereof, such as humanized or chimericantibodies. Antiidiotypic antibodies specific for the idiotype of ananti-B7-DC antibody are also included. The term “antibody” is meant toinclude both intact molecules as well as fragments thereof that includethe antigen-binding site and are capable of binding to a B7-DC epitope.These include, Fab and F(ab′)₂ fragments which lack the Fc fragment ofan intact antibody, clear more rapidly from the circulation, and mayhave less non-specific tissue binding than an intact antibody (Wahl etal., J. Nuc. Med. 24:316-325 (1983)). Also included are Fv fragments(Hochman, J et al. (1973) Biochemistry 12:1130-1135; Sharon, J. et al.(1976) Biochemistry 15:1591-1594). These various fragments are producedusing conventional techniques such as protease cleavage or chemicalcleavage (see, e.g., Rousseaux et al., Meth. Enzymol., 121:663-69(1986)).

Polyclonal antibodies are obtained as sera from immunized animals suchas rabbits, goats, rodents, etc. and may be used directly withoutfurther treatment or may be subjected to conventional enrichment orpurification methods such as ammonium sulfate precipitation, ionexchange chromatography, and affinity chromatography.

The immunogen may comprise the complete B7-DC protein, or fragments orderivatives thereof. Preferred immunogens comprise all or a part of theextracellular domain (ECD) of human B7-DC, where these residues containthe post-translation modifications, such as glycosylation, found on thenative B7-DC. Immunogens comprising the extracellular domain areproduced in a variety of ways known in the art, e.g., expression ofcloned genes using conventional recombinant methods, isolation fromcells of origin, cell populations expressing high levels of B7-DC, etc.

Monoclonal antibodies may be produced using conventional hybridomatechnology, such as the procedures introduced by Kohler and Milstein(Nature, 256:495-97 (1975)), and modifications thereof (see abovereferences). An animal, preferably a mouse is primed by immunizationwith an immunogen as above to elicit the desired antibody response inthe primed animal. B lymphocytes from the lymph nodes, spleens orperipheral blood of a primed, animal are fused with myeloma cells,generally in the presence of a fusion promoting agent such aspolyethylene glycol (PEG). Any of a number of murine myeloma cell linesare available for such use; the P3-NS1/1-Ag4-1, P3-x63-k0Ag8.653,Sp2/0-Ag14, or HL1-653 myeloma lines (available from the ATCC,Rockville, Md.). Subsequent steps include growth in selective medium sothat unfused parental myeloma cells and donor lymphocyte cellseventually die while only the hybridoma cells survive. These are clonedand grown and their supernatants screened for the presence of antibodyof the desired specificity, e.g. by immunoassay techniques using B7-DCfusion proteins. Positive clones are subcloned, e.g., by limitingdilution, and the monoclonal antibodies are isolated.

Hybridomas produced according to these methods can be propagated invitro or in vivo (in ascites fluid) using techniques known in the art(see generally Fink et al., Prog. Clin. Pathol., 9:121-33 (1984)).Generally, the individual cell line is propagated in culture and theculture medium containing high concentrations of a single monoclonalantibody can be harvested by decantation, filtration, or centrifugation.

The antibody may be produced as a single chain antibody or scFv insteadof the normal multimeric structure. Single chain antibodies include thehypervariable regions from an Ig of interest and recreate the antigenbinding site of the native Ig while being a fraction of the size of theintact Ig (Skerra, A. et al. (1988) Science, 240: 1038-1041; Pluckthun,A. et al. (1989) Methods Enzymol. 178: 497-515; Winter, G. et al. (1991)Nature, 349: 293-299). In a preferred embodiment, the antibody isproduced using conventional molecular biology techniques.

E. Immunogenic Compositions

Vaccines require strong T cell response to eliminate cancer cells andinfected cells. Variant B7-DC variants described herein can beadministered as a component of a vaccine to provide a costimulatorysignal to T cells. Vaccines disclosed herein include antigens, a sourceof variant B7-DC polypeptides and optionally adjuvants and targetingmolecules. Sources of variant B7-DC polypeptides include any variantB7-DC polypeptide, variant B7-DC fusion proteins, nucleic acids encodingvariant B7-DC polypeptides or variant B7-DC fusion proteins, or hostcells containing vectors that express B7-DC polypeptides or variantB7-DC fusion proteins.

1. Antigens

Antigens can be peptides, proteins, polysaccharides, saccharides,lipids, nucleic acids, or combinations thereof. The antigen can bederived from a virus, bacterium, parasite, plant, protozoan, fungus,tissue or transformed cell such as a cancer or leukemic cell and can bea whole cell or immunogenic component thereof e.g., cell wall componentsor molecular components thereof.

Suitable antigens are known in the art and are available from commercialgovernment and scientific sources. In one embodiment, the antigens arewhole inactivated or attenuated organisms. These organisms may beinfectious organisms, such as viruses, parasites and bacteria. Theseorganisms may also be tumor cells. The antigens may be purified orpartially purified polypeptides derived from tumors or viral orbacterial sources. The antigens can be recombinant polypeptides producedby expressing DNA encoding the polypeptide antigen in a heterologousexpression system. The antigens can be DNA encoding all or part of anantigenic protein. The DNA may be in the form of vector DNA such asplasmid DNA.

Antigens may be provided as single antigens or may be provided incombination. Antigens may also be provided as complex mixtures ofpolypeptides or nucleic acids.

i. Viral Antigens

A viral antigen can be isolated from any virus including, but notlimited to, a virus from any of the following viral families:Arenaviridae, Arterivirus, Astroviridae, Baculoviridae, Badnavirus,Barnaviridae, Birnaviridae, Bromoviridae, Bunyaviridae, Caliciviridae,Capillovirus, Carlavirus, Caulimovirus, Circoviridae, Closterovirus,Comoviridae, Coronaviridae (e.g., Coronavirus, such as severe acuterespiratory syndrome (SARS) virus), Corticoviridae, Cystoviridae,Deltavirus, Dianthovirus, Enamovirus, Filoviridae (e.g., Marburg virusand Ebola virus (e.g., Zaire, Reston, Ivory Coast, or Sudan strain)),Flaviviridae, (e.g., Hepatitis C virus, Dengue virus 1, Dengue virus 2,Dengue virus 3, and Dengue virus 4), Hepadnaviridae, Herpesviridae(e.g., Human herpesvirus 1, 3, 4, 5, and 6, and Cytomegalovirus),Hypoviridae, Iridoviridae, Leviviridae, Lipothrixviridae, Microviridae,Orthomyxoviridae (e.g., Influenzavirus A and B and C), Papovaviridae,Paramyxoviridae (e.g., measles, mumps, and human respiratory syncytialvirus), Parvoviridue, Picornaviridae (e.g., poliovirus, rhinovirus,hepatovirus, and aphthovirus), Poxviridae (e.g., vaccinia and smallpoxvirus), Reoviridae (e.g., rotavirus), Retroviridae (e.g., lentivirus,such as human immunodeficiency virus (HIV) 1 and HIV 2), Rhabdoviridae(for example, rabies virus, measles virus, respiratory syncytial virus,etc.), Togaviridae (for example, rubella virus, dengue virus, etc.), andTotivridae. Suitable viral antigens also include all or part of Dengueprotein M, Dengue protein E, Dengue D1NS1, Dengue D1NS2, and DengueD1NS3.

Viral antigens may be derived from a particular strain such as apapilloma virus, a herpes virus, i.e. herpes simplex 1 and 2; ahepatitis virus, for example, hepatitis A virus (HAV), hepatitis B virus(HBV), hepatitis C virus (HCV), the delta hepatitis D virus (HDV),hepatitis E virus (HEV) and hepatitis G virus (HGV), the tick-borneencephalitis viruses; parainfluenza, varicella-zoster, cytomeglavirus,Epstein-Barr, rotavirus, rhinovirus, adenovirus, coxsackieviruses,equine encephalitis, Japanese encephalitis, yellow fever, Rift Valleyfever, and lymphocytic choriomeningitis.

ii. Bacterial Antigens

Bacterial antigens can originate from any bacteria including, but notlimited to, Actinomyces, Anabaena, Bacillus, Bacteroides, Bdellovibrio,Bordetella, Borrelia, Campylobacter, Caulobacter, Chlamydia, Chlorobium,Chromatium, Clostridium, Corynebacterium, Cytophaga, Deinococcus,Escherichia, Francisella, Halobacterium, Heliobacter, Haemophilus,Hemophilus influenza type B (HIB), Hyphomicrobium, Legionella,Leptspirosis, Listeria, Meningococcus A, B and C, Methanobacterium,Micrococcus, Myobacterium, Mycoplasma, Myxococcus, Neisseria,Nitrobacter, Oscillatoria, Prochloron, Proteus, Pseudomonas,Phodospirillum, Rickettsia, Salmonella, Shigella, Spirillum,Spirochaeta, Staphylococcus, Streptococcus, Streptomyces, Sulfolobus,Thermoplasma, Thiobacillus, and Treponema, Vibrio, and Yersinia.

iii. Parasite Antigens

Parasite antigens can be obtained from parasites such as, but notlimited to, an antigen derived from Cryptococcus neoformans, Histoplasmacapsulatum, Candida albicans, Candida tropicalis, Nocardia asteroides,Rickettsia ricketsii Rickettsia typhi, Mycoplasma pneumoniae, Chlamydialpsittaci, Chlamydial trachomatis, Plasmodium falciparum, Trypanosomabrucei, Entamoeba histolytica, Toxoplasma gondii, Trichomonas vaginalisand Schistosoma mansoni. These include Sporozoan antigens, Plasmodianantigens, such as all or part of a Circumsporozoite protein, aSporozoite surface protein, a liver stage antigen, an apical membraneassociated protein, or a Merozoite surface protein.

iv. Allergens and Environmental Antigens

The antigen can be an allergen or environmental antigen, such as, butnot limited to, an antigen derived from naturally occurring allergenssuch as pollen allergens (tree-, herb, weed-, and grass pollenallergens), insect allergens (inhalant, saliva and venom allergens),animal hair and dandruff allergens, and food allergens. Important pollenallergens from trees, grasses and herbs originate from the taxonomicorders of Fagales, Oleales, Pinales and platanaceae including i.a. birch(Betula), alder (Alnus), hazel (Corylus), hornbeam (Carpinus) and olive(Olea), cedar (Cryptomeria and Juniperus), Plane tree (Platanus), theorder of Poales including i.e. grasses of the genera Lolium, Phleum,Poa, Cynodon, Dactylis, Holcus, Phalaris, Secale, and Sorghum, theorders of Asterales and Urticales including i.a. herbs of the generaAmbrosia, Artemisia, and Parietaria. Other allergen antigens that may beused include allergens from house dust mites of the genusDermatophagoides and Euroglyphus, storage mite e.g Lepidoglyphys,Glycyphagus and Tyrophagus, those from cockroaches, midges and flease.g. Blatella, Periplaneta, Chironomus and Ctenocepphalides, those frommammals such as cat, dog and horse, birds, venom allergens includingsuch originating from stinging or biting insects such as those from thetaxonomic order of Hymenoptera including bees (superfamily Apidae),wasps (superfamily Vespidea), and ants (superfamily Formicoidae). Stillother allergen antigens that may be used include inhalation allergensfrom fungi such as from the genera Alternaria and Cladosporium.

v. Tumor Antigens

The antigen can be a tumor antigen, including a tumor-associated ortumor-specific antigen, such as, but not limited to, alpha-actinin-4,Bcr-Abl fusion protein, Casp-8, beta-catenin, cdc27, cdk4, cdkn2a,coa-1, dek-can fusion protein, EF2, ETV6-AML1 fusion protein,LDLR-fucosyltransferaseAS fusion protein, HLA-A2, HLA-A11, hsp70-2,KIAA0205, Mart2, Mum-1,2, and 3, neo-PAP, myosin class I, OS-9, pm1-RARαfusion protein, PTPRK, K-ras, N-ras, Triosephosphate isomeras, Bage-1,Gage 3,4,5,6,7, GnTV, Herv-K-mel, Lage-1, Mage-A1, 2,3,4,6,10,12,Mage-C2, NA-88, NY-Eso-1/Lage-2, SP17, SSX-2, and TRP2-Int2, MelaA(MART-I), gp100 (Pmel 17), tyrosinase, TRP-1, TRP-2, MACE-1, MAGE-3,BAGE, GAGE-1, GAGE-2, p15(58), CEA, RAGE, NY-ESO (LAGE), SCP-1,Hom/Mel-40, PRAME, p53, H-Ras, HER-2/neu, BCR-ABL, E2A-PRL, H4-RET,IGH-IGK, MYL-RAR, Epstein Barr virus antigens, EBNA, humanpapillomavirus (HPV) antigens E6 and E7, TSP-180, MAGE-4, MAGE-5,MAGE-6, p185erbB2, p180erbB-3, c-met, nm-23H1, PSA, TAG-72-4, CA 19-9,CA 72-4, CAM 17.1, NuMa, K-ras, β-Catenin, CDK4, Mum-1, p16, TAGE, PSMA,PSCA, CT7, telomerase, 43-9F, 5T4, 791Tgp72, α-fetoprotein, 13HCG,BCA225, BTAA, CA 125, CA 15-3 (CA 27.29\BCAA), CA 195, CA 242, CA-50,CAM43, CD68\KP1, CO-029, FGF-5, G250, Ga733 (EpCAM), HTgp-175, M344,MA-50, MG7-Ag, MOV18, NB\70K, NY-CO-1, RCAS1, SDCCAG16, TA-90 (Mac-2binding protein\cyclophilin C-associated protein), TAAL6, TAG72, TLP,and TPS.

2. Targeting Molecules

Of the main types of antigen-presenting cells (B cell, macrophages anddendritic cells (DCs)), the DC is the most potent and is responsible forinitiating all antigen-specific immune responses. Thus, targeting DCsprovides the opportunity to enhance the delivery of antigen and antigenresponses.

Dendritic cells express a number of cell surface receptors that canmediate the endocytosis of bound antigen. Targeting exogenous antigensto internalizing surface molecules on systemically-distributed antigenpresenting cells facilitates uptake of antigens and thus overcomes amajor rate-limiting step in immunization and thus in vaccination.

Dendritic cell targeting molecules include monoclonal or polyclonalantibodies or fragments thereof that recognize and bind to epitopesdisplayed on the surface of dendritic cells. Dendritic cell targetingmolecules also include ligands which bind to a cell surface receptor ondendritic cells. One such receptor, the lectin DEC-205, has been used invitro and in mice to boost both humoral (antibody-based) and cellular(CD8 T cell) responses by 2-4 orders of magnitude (Hawiger, et al., J.Exp. Med., 194(6):769-79 (2001); Bonifaz, et al., J. Exp. Med,196(12):1627-38 (2002); Bonifaz, et al., J. Exp. Med., 199(6):815-24(2004)). In these experiments, antigens were fused to an anti-DEC205heavy chain and a recombinant antibody molecule was used forimmunization.

A variety of other endocytic receptors, including a mannose-specificlectin (mannose receptor) and IgG Fc receptors, have also been targetedin this way with similar enhancement of antigen presentation efficiency.Other suitable receptors which may be targeted include, but are notlimited to, DC-SIGN, 33D1, SIGLEC-H, DCIR, CD11c, heat shock proteinreceptors and scavenger receptors.

Other receptors which may be targeted include the toll-like receptors(TLRs). TLRs recognize and bind to pathogen-associated molecularpatterns (PAMPs). PAMPs target the TLR on the surface of the dendriticcell and signals internally, thereby potentially increasing DC antigenuptake, maturation and T-cell stimulatory capacity. PAMPs conjugated tothe particle surface or co-encapsulated include unmethylated CpG DNA(bacterial), double-stranded RNA (viral), lipopolysachamide (bacterial),peptidoglycan (bacterial), lipoarabinomannin (bacterial), zymosan(yeast), mycoplasmal lipoproteins such as MALP-2 (bacterial), flagellin(bacterial) poly(inosinic-cytidylic) acid (bacterial), lipoteichoic acid(bacterial) or imidazoquinolines (synthetic).

3. Adjuvants

Optionally, the vaccines described herein may include adjuvants. Theadjuvant can be, but is not limited to, one or more of the following:oil emulsions (e.g., Freund's adjuvant); saponin formulations; virosomesand viral-like particles; bacterial and microbial derivatives;immunostimulatory oligonucleotides; ADP-ribosylating toxins anddetoxified derivatives; alum; BCG; mineral-containing compositions(e.g., mineral salts, such as aluminium salts and calcium salts,hydroxides, phosphates, sulfates, etc.); bioadhesives and/ormucoadhesives; microparticles; liposomes; polyoxyethylene ether andpolyoxyethylene ester formulations; polyphosphazene; muramyl peptides;imidazoquinolone compounds; and surface active substances (e.g.lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions,keyhole limpet hemocyanin, and dinitrophenol).

Adjuvants may also include immunomodulators such as cytokines,interleukins (e.g., IL-1, IL-2, IL-4, IL-5, IL-6, IL-7, IL-12, etc.),interferons (e.g., interferon-.gamma.), macrophage colony stimulatingfactor, and tumor necrosis factor. In addition to variant B7-DCpolypeptides, other co-stimulatory molecules, including otherpolypeptides of the B7 family, may be administered. Such proteinaceousadjuvants may be provided as the full-length polypeptide or an activefragment thereof, or in the form of DNA, such as plasmid DNA.

F. Pharmaceutical Compositions

Pharmaceutical compositions including variant B7-DC polypeptides,variant B7-DC fusion proteins, nucleic acids encoding variant B7-DCpolypeptides and fusion proteins, and vectors containing the same areprovided. The pharmaceutical compositions may be for administration byoral, parenteral (intramuscular, intraperitoneal, intravenous (IV) orsubcutaneous injection), transdermal (either passively or usingiontophoresis or electroporation), transmucosal (nasal, vaginal, rectal,or sublingual) routes of administration or using bioerodible inserts andcan be formulated in dosage forms appropriate for each route ofadministration. In a preferred embodiment, the peptides are administeredin an aqueous solution, particularly for parenteral injection. Ingeneral, pharmaceutical compositions are provided including effectiveamounts of a variant B7-DC polypeptide, fusion proteinor nucleic acidencoding the same, or derivative products, and pharmaceuticallyacceptable diluents, preservatives, solubilizers, emulsifiers, adjuvantsand/or carriers. Such compositions include diluents of various buffercontent (e.g., Tris-HCl, acetate, phosphate), pH and ionic strength;additives such as detergents and solubilizing agents (e.g., TWEEN 20,TWEEN 80, Polysorbate 80), anti-oxidants (e.g., ascorbic acid, sodiummetabisulfite), preservatives (e.g., Thimersol, benzyl alcohol) andbulking substances (e.g., lactose, mannitol); incorporation of thematerial into particulate preparations of polymeric compounds such aspolylactic acid, polyglycolic acid, etc. or into liposomes. Hylauronicacid may also be used. Such compositions may influence the physicalstate, stability, rate of in vivo release, and rate of in vivo clearanceof the present proteins and derivatives. See, e.g., Remington'sPharmaceutical Sciences, 18th Ed. (1990, Mack Publishing Co., Easton,Pa. 18042) pages 1435-1712 which are herein incorporated by reference.The compositions may be prepared in liquid form, or may be in driedpowder (e.g., lyophilized) form.

1. Oral Delivery

Variant B7-DC polypeptides, fusion proteins and nucleic acids encodingthe same can be formulated for oral delivery. Oral solid dosage formsare described generally in Remington's Pharmaceutical Sciences, 18th Ed.1990 (Mack Publishing Co. Easton Pa. 18042) at Chapter 89, which isherein incorporated by reference. Solid dosage forms include tablets,capsules, pills, troches or lozenges, cachets, pellets, powders, orgranules. Also, liposomal or proteinoid encapsulation may be used toformulate the present compositions (as, for example, proteinoidmicrospheres reported in U.S. Pat. No. 4,925,673). Liposomalencapsulation may be used and the liposomes may be derivatized withvarious polymers (e.g., U.S. Pat. No. 5,013,556). A description ofpossible solid dosage forms for the therapeutic is given by Marshall, K.In: Modern Pharmaceutics Edited by G. S. Banker and C. T. Rhodes Chapter10, 1979, herein incorporated by reference. In general, the formulationwill include the ABC transporter ligands (or chemically modified formsthereof) and inert ingredients which allow for protection against thestomach environment, and release of the biologically active material inthe intestine.

Another embodiment provides liquid dosage forms for oral administration,including pharmaceutically acceptable emulsions, solutions, suspensions,and syrups, which may contain other components including inert diluents;adjuvants such as wetting agents, emulsifying and suspending agents; andsweetening, flavoring, and perfuming agents.

The polypeptide antagonists may be chemically modified so that oraldelivery of the derivative is efficacious. Generally, the chemicalmodification contemplated is the attachment of at least one moiety tothe component molecule itself, where said moiety permits (a) inhibitionof proteolysis; and (b) uptake into the blood stream from the stomach orintestine. Also desired is the increase in overall stability of thecomponent or components and increase in circulation time in the body.PEGylation is a preferred chemical modification for pharmaceuticalusage. Other moieties that may be used include: propylene glycol,copolymers of ethylene glycol and propylene glycol, carboxymethylcellulose, dextran, polyvinyl alcohol, polyvinyl pyrrolidone,polyproline, poly-1,3-dioxolane and poly-1,3,6-tioxocane [see, e.g.,Abuchowski and Davis (1981) “Soluble Polymer-Enzyme Adducts,” in Enzymesas Drugs. Hocenberg and Roberts, eds. (Wiley-Interscience: New York,N.Y.) pp. 367-383; and Newmark, et al. (1982) J. Appl. Biochem.4:185-189].

For oral formulations, the location of release may be the stomach, thesmall intestine (the duodenum, the jejunem, or the ileum), or the largeintestine. One skilled in the art has available formulations which willnot dissolve in the stomach, yet will release the material in theduodenum or elsewhere in the intestine. Preferably, the release willavoid the deleterious effects of the stomach environment, either byprotection of the peptide (or derivative) or by release of the peptide(or derivative) beyond the stomach environment, such as in theintestine.

To ensure full gastric resistance a coating impermeable to at least pH5.0 is essential. Examples of the more common inert ingredients that areused as enteric coatings are cellulose acetate trimellitate (CAT),hydroxypropylmethylcellulose phthalate (HPMCP), HPMCP 50, HPMCP 55,polyvinyl acetate phthalate (PVAP), Eudragit L30D, Aquateric, celluloseacetate phthalate (CAP), Eudragit L, Eudragit S, and Shellac. Thesecoatings may be used as mixed films.

A coating or mixture of coatings can also be used on tablets, which arenot intended for protection against the stomach. This can include sugarcoatings, or coatings which make the tablet easier to swallow. Capsulesmay consist of a hard shell (such as gelatin) for delivery of drytherapeutic (i.e. powder), for liquid forms a soft gelatin shell may beused. The shell material of cachets could be thick starch or otheredible paper. For pills, lozenges, molded tablets or tablet triturates,moist massing techniques can be used.

The variant B7-DC polypeptide, variant B7-DC fusion protein or nucleicacid encoding the same (or derivative) can be included in theformulation as fine multiparticulates in the form of granules or pelletsof particle size about 1 mm. The formulation of the material for capsuleadministration could also be as a powder, lightly compressed plugs, oreven as tablets. These therapeutics could be prepared by compression.

Colorants and/or flavoring agents may also be included. For example, thesH4 antagonist (or derivative) may be formulated (such as by liposome ormicrosphere encapsulation) and then further contained within an edibleproduct, such as a refrigerated beverage containing colorants andflavoring agents.

One may dilute or increase the volume of the variant B7-DC polypeptide,variant B7-DC fusion protein or nucleic acid encoding the same (orderivative) with an inert material. These diluents could includecarbohydrates, especially mannitol, α-lactose, anhydrous lactose,cellulose, sucrose, modified dextrans and starch. Certain inorganicsalts may be also be used as fillers including calcium triphosphate,magnesium carbonate and sodium chloride. Some commercially availablediluents are Fast-Flo, Emdex, STA-Rx 1500, Emcompress and Avicell.

Disintegrants may be included in the formulation of the therapeutic intoa solid dosage form. Materials used as disintegrates include but are notlimited to starch, including the commercial disintegrant based onstarch, Explotab Sodium starch glycolate, Amberlite, sodiumcarboxymethylcellulose, ultramylopectin, sodium alginate, gelatin,orange peel, acid carboxymethyl cellulose, natural sponge and bentonitemay all be used. The disintegrants may also be insoluble cationicexchange resins. Powdered gums may be used as disintegrants and asbinders and can include powdered gums such as agar, Karaya ortragacanth. Alginic acid and its sodium salt are also useful asdisintegrants.

Binders may be used to hold the variant B7-DC polypeptide, variant B7-DCfusion protein or nucleic acid encoding the same (or derivative)together to form a hard tablet and include materials from naturalproducts such as acacia, tragacanth, starch and gelatin. Others includemethyl cellulose (MC), ethyl cellulose (EC) and carboxymethyl cellulose(CMC). Polyvinyl pyrrolidone (PVP) and hydroxypropylmethyl cellulose(HPMC) could both be used in alcoholic solutions to granulate thepeptide (or derivative).

An antifrictional agent may be included in the formulation of the sH4antagonist (or derivative) to prevent sticking during the formulationprocess. Lubricants may be used as a layer between the peptide (orderivative) and the die wall, and these can include but are not limitedto; stearic acid including its magnesium and calcium salts,polytetrafluoroethylene (PTFE), liquid paraffin, vegetable oils andwaxes. Soluble lubricants may also be used such as sodium laurylsulfate, magnesium lauryl sulfate, polyethylene glycol of variousmolecular weights, Carbowax 4000 and 6000.

Glidants that might improve the flow properties of the drug duringformulation and to aid rearrangement during compression might be added.The glidants may include starch, tale, pyrogenic silica and hydratedsilicoaluminate.

To aid dissolution of the peptide (or derivative) into the aqueousenvironment a surfactant might be added as a wetting agent. Surfactantsmay include anionic detergents such as sodium lauryl sulfate, dioctylsodium sulfosuccinate and dioctyl sodium sulfonate. Cationic detergentsmight be used and could include benzalkonium chloride or benzethomiumchloride. The list of potential nonionic detergents that could beincluded in the formulation as surfactants are lauromacrogol 400,polyoxyl 40 stearate, polyoxyethylene hydrogenated castor oil 10, 50 and60, glycerol monostearate, polysorbate 20, 40, 60, 65 and 80, sucrosefatty acid ester, methyl cellulose and carboxymethyl cellulose. Thesesurfactants could be present in the formulation of the protein orderivative either alone or as a mixture in different ratios.

Additives which potentially enhance uptake of the variant B7-DCpolypeptide, variant B7-DC fusion protein or nucleic acid encoding thesame (or derivative) are for instance the fatty acids oleic acid,linoleic acid and linolenic acid.

Controlled release oral formulations may be desirable. The variant B7-DCpolypeptide, variant B7-DC fusion protein or nucleic acid encoding thesame (or derivative) could be incorporated into an inert matrix whichpermits release by either diffusion or leaching mechanisms, e.g., gums.Slowly degenerating matrices may also be incorporated into theformulation. Some enteric coatings also have a delayed release effect.Another form of a controlled release is by a method based on the Orostherapeutic system (Alza Corp.), i.e. the drug is enclosed in asemipermeable membrane which allows water to enter and push drug outthrough a single small opening due to osmotic effects.

Other coatings may be used for the formulation. These include a varietyof sugars which could be applied in a coating pan. The variant B7-DCpolypeptide, variant B7-DC fusion protein or nucleic acid encoding thesame (or derivative) could also be given in a film coated tablet and thematerials used in this instance are divided into 2 groups. The first arethe nonenteric materials and include methyl cellulose, ethyl cellulose,hydroxyethyl cellulose, methylhydroxy-ethyl cellulose, hydroxypropylcellulose, hydroxypropyl-methyl cellulose, sodium carboxy-methylcellulose, providone and the polyethylene glycols. The second groupconsists of the enteric materials that are commonly esters of phthalicacid.

A mix of materials might be used to provide the optimum film coating.Film coating may be carried out in a pan coater or in a fluidized bed orby compression coating.

2. Parenteral Delivery

Preparations according to this invention for parenteral administrationinclude sterile aqueous or non-aqueous solutions, suspensions, oremulsions. Examples of non-aqueous solvents or vehicles are propyleneglycol, polyethylene glycol, vegetable oils, such as olive oil and cornoil, gelatin, and injectable organic esters such as ethyl oleate. Suchdosage forms may also contain adjuvants such as preserving, wetting,emulsifying, and dispersing agents. They may be sterilized by, forexample, filtration through a bacteria retaining filter, byincorporating sterilizing agents into the compositions, by irradiatingthe compositions, or by heating the compositions. They can also bemanufactured using sterile water, or some other sterile injectablemedium, immediately before use.

3. Mucous Membrane Delivery

Compositions for rectal or vaginal administration are preferablysuppositories which may contain, in addition to the active substance,excipients such as cocoa butter or a suppository wax. Compositions fornasal or sublingual administration are also prepared with standardexcipients well known in the art (see below).

4. Pulmonary Delivery

Also contemplated herein is pulmonary delivery of the sH4 antagonists(or derivatives thereof). The variant B7-DC polypeptide, variant B7-DCfusion protein or nucleic acid encoding the same (or derivative) isdelivered to the lungs of a mammal while inhaling and traverses acrossthe lung epithelial lining to the blood stream (see, e.g., Adjei, et al.(1990) Pharmaceutical Research 7:565-569; Adjei, et al. (1990) Int. J.Pharmaceutics 63:135-144 (leuprolide acetate); Braquet, et al. (1989) J.Cardiovascular Pharmacology 13 (sup5):143-146 (endothelin-1); Hubbard,et al. (1989) Annals of Internal Medicine, Vol. III, pp. 206-212(α1-antitrypsin); Smith, et al. (1989) J. Clin. Invest. 84:1145-1146(alpha-1-proteinase); Oswein, et al. (1990) “Aerosolization ofProteins”, Proceedings of Symposium on Respiratory Drug Delivery IIKeystone, Colo. (recombinant human growth hormone); Debs, et al. (1988)J. Immunol. 140:3482-3488 (interferon-.gamma. and tumor necrosis factoralpha); and U.S. Pat. No. 5,284,656 to Platz, et al. (granulocyte colonystimulating factor). A method and composition for pulmonary delivery ofdrugs for systemic effect is described in U.S. Pat. No. 5,451,569 toWong, et al.

A wide range of mechanical devices designed for pulmonary delivery oftherapeutic products can be used, including but not limited tonebulizers, metered dose inhalers, and powder inhalers, all of which arefamiliar to those skilled in the art. Some specific examples ofcommercially available devices suitable for the practice of thisinvention are the Ultravent nebulizer (Mallinckrodt Inc., St. Louis,Mo.); the Acorn II nebulizer (Marquest Medical Products, Englewood,Colo.); the Ventolin metered dose inhaler (Glaxo Inc., Research TrianglePark, N.C.); and the Spinhaler powder inhaler (Fisons Corp., Bedford,Mass.).

All such devices require the use of formulations suitable for thedispensing of the variant B7-DC polypeptide, variant B7-DC fusionprotein or nucleic acid encoding the same (or derivative). Typically,each formulation is specific to the type of device employed and mayinvolve the use of an appropriate propellant material, in addition tothe usual diluents, adjuvants and/or carriers useful in therapy. Also,the use of liposomes, microcapsules or microspheres, inclusioncomplexes, or other types of carriers is contemplated. Chemicallymodified peptides may also be prepared in different formulationsdepending on the type of chemical modification or the type of deviceemployed.

Formulations suitable for use with a nebulizer, either jet orultrasonic, will typically comprise peptide (or derivative) dissolved inwater at a concentration of about 0.1 to 25 mg of biologically activeprotein per mL of solution. The formulation may also include a bufferand a simple sugar (e.g., for protein stabilization and regulation ofosmotic pressure). The nebulizer formulation may also contain asurfactant, to reduce or prevent surface induced aggregation of thepeptide (or derivative) caused by atomization of the solution in formingthe aerosol.

Formulations for use with a metered-dose inhaler device will generallyinclude a finely divided powder containing the peptide (or derivative)suspended in a propellant with the aid of a surfactant. The propellantmay be any conventional material employed for this purpose, such as achlorofluorocarbon, a hydrochlorofluorocarbon, a hydrofluorocarbon, or ahydrocarbon, including trichlorofluoromethane, dichlorodifluoromethane,dichlorotetrafluoroethanol, and 1,1,1,2-tetrafluoroethane, orcombinations thereof. Suitable surfactants include sorbitan trioleateand soya lecithin. Oleic acid may also be useful as a surfactant.

Formulations for dispensing from a powder inhaler device will include afinely divided dry powder containing peptide (or derivative) and mayalso include a bulking agent, such as lactose, sorbitol, sucrose, ormannitol in amounts which facilitate dispersal of the powder from thedevice, e.g., 50 to 90% by weight of the formulation. The variant B7-DCpolypeptide, variant B7-DC fusion protein or nucleic acid encoding thesame (or derivative) should most advantageously be prepared inparticulate form with an average particle size of less than 10 mm (ormicrons), most preferably 0.5 to 5 mm, for most effective delivery tothe distal lung.

5. Polymeric Matrices

Both non-biodegradable and biodegradable matrices can be used fordelivery of variant B7-DC polypeptides, variant B7-DC fusion proteins ornucleic acids encoding the same, although biodegradable matrices arepreferred. These may be natural or synthetic polymers, althoughsynthetic polymers are preferred due to the better characterization ofdegradation and release profiles. The polymer is selected based on theperiod over which release is desired. In some cases linear release maybe most useful, although in others a pulse release or “bulk release” mayprovide more effective results. The polymer may be in the form of ahydrogel (typically in absorbing up to about 90% by weight of water),and can optionally be crosslinked with multivalent ions or polymers.

Representative synthetic polymers that can be used for delivery includepolyamides, polycarbonates, polyalkylenes, polyalkylene glycols,polyalkylene oxides, polyalkylene terepthalates, polyvinyl alcohols,polyvinyl ethers, polyvinyl esters, polyvinyl halides,polyvinylpyrrolidone, polyglycolides, polysiloxanes, polyurethanes andco-polymers thereof, alkyl cellulose, hydroxyalkyl celluloses, celluloseethers, cellulose esters, nitro celluloses, polymers of acrylic andmethacrylic esters, methyl cellulose, ethyl cellulose, hydroxypropylcellulose, hydroxy-propyl methyl cellulose, hydroxybutylmethylcellulose, cellulose acetate, cellulose propionate, celluloseacetate butyrate, cellulose acetate phthalate, carboxylethyl cellulose,cellulose triacetate, cellulose sulphate sodium salt, poly(methylmethacrylate), poly(ethyl methacrylate), poly(butylmethacrylate),poly(isobutyl methacrylate), poly(hexylmethacrylate), poly(isodecylmethacrylate), poly(lauryl methacrylate), poly(phenyl methacrylate),poly(methyl acrylate), poly(isopropyl acrylate), poly(isobutylacrylate), poly(octadecyl acrylate), polyethylene, polypropylene,poly(ethylene glycol), poly(ethylene oxide), poly(ethyleneterephthalate), poly(vinyl alcohols), poly(vinyl acetate, poly vinylchloride, polystyrene and polyvinylpyrrolidone.

Examples of non-biodegradable polymers include ethylene vinyl acetate,poly(meth)acrylic acid, polyamides, copolymers and mixtures thereof.Examples of biodegradable polymers include synthetic polymers such aspolymers of lactic acid and glycolic acid, polyanhydrides,poly(ortho)esters, polyurethanes, poly(butic acid), poly(valeric acid),and poly(lactide-co-caprolactone), and natural polymers such as alginateand other polysaccharides including dextran and cellulose, collagen,chemical derivatives thereof (substitutions, additions of chemicalgroups, for example, alkyl, alkylene, hydroxylations, oxidations, andother modifications routinely made by those skilled in the art), albuminand other hydrophilic proteins, zein and other prolamines andhydrophobic proteins, copolymers and mixtures thereof. In general, thesematerials degrade either by enzymatic hydrolysis or exposure to water invivo, by surface or bulk erosion.

Bioadhesive polymers of particular interest include bioerodiblehydrogels described by H. S. Sawhney, C. P. Pathak and J. A. Hubell inMacromolecules, 1993, 26, 581-587, polyhyaluronic acids, casein,gelatin, glutin, polyanhydrides, polyacrylic acid, alginate, chitosan,poly(methyl methacrylates), poly(ethyl methacrylates),poly(butylmethaerylate), poly (isobutyl methacrylate),poly(hexylmethacrylate), poly(isodecyl methacrylate), poly(laurylmethacrylate), poly(phenyl methacrylate), poly(methyl acrylate),poly(isopropyl acrylate), poly(isobutyl acrylate), and poly(octadecylacrylate).

The matrix can be in the form of microparticles such as microspheres,where peptides are dispersed within a solid polymeric matrix ormicrocapsules, where the core is of a different material than thepolymeric shell, and the peptide is dispersed or suspended in the core,which may be liquid or solid in nature. Unless specifically definedherein, microparticles, microspheres, and microcapsules are usedinterchangeably. Alternatively, the polymer may be cast as a thin slabor film, ranging from nanometers to four centimeters, a powder producedby grinding or other standard techniques, or even a gel such as ahydrogel.

The matrices can be formed by solvent evaporation, spray drying, solventextraction and other methods known to those skilled in the art.

Bioerodible microspheres can be prepared using any of the methodsdeveloped for making microspheres for drug delivery, for example, asdescribed by Mathiowitz and Langer, J. Controlled Release 5, 13-22(1987); Mathiowitz, et al., Reactive Polymers 6, 275-283 (1987); andMathiowitz, et al., J. Appl. Polymer Sci. 35, 755-774 (1988). Theselection of the method depends on the polymer selection, the size,external morphology, and crystallinity that is desired, as described,for example, by Mathiowitz, et al., Scanning Microscopy 4, 329-340(1990); Mathiowitz, et al., J. Appl. Polymer Sci. 45, 125-134 (1992);and Benita, et al., J. Pharm. Sci. 73, 1721-1724 (1984). In solventevaporation, described for example, in Mathiowitz, et al., (1990),Benita, and U.S. Pat. No. 4,272,398 to Jaffe, the polymer is dissolvedin a volatile organic solvent. The anagonist either in soluble form ordispersed as fine particles, is added to the polymer solution, and themixture is suspended in an aqueous phase that contains a surface activeagent such as poly(vinyl alcohol). The resulting emulsion is stirreduntil most of the organic solvent evaporates, leaving solidmicrospheres. In general, the polymer can be dissolved in methylenechloride. Microspheres with different sizes (1-1000 microns) andmorphologies can be obtained by this method which is useful forrelatively stable polymers such as polyesters and polystyrene. However,labile polymers such as polyanhydrides may degrade due to exposure towater. For these polymers, hot melt encapsulation and solvent removalmay be preferred.

In hot melt encapsulation, the polymer is first melted and then mixedwith the solid particles of variant B7-DC polypeptide, variant B7-DCfusion protein or nucleic acid encoding the same. The mixture issuspended in a non-miscible solvent such as silicon oil and, withcontinuous stirring, heated to 5° C. above the melting point of thepolymer. Once the emulsion is stabilized, it is cooled until the polymerparticles solidify. The resulting microspheres are washed by decantationwith petroleum ether to give a free-flowing powder. Microspheres withdiameters between one and 1000 microns can be obtained with this method.The external surface of spheres prepared with this technique is usuallysmooth and dense. This procedure is useful with water labile polymers,but is limited to use with polymers with molecular weights between 1000and 50000. Solvent removal was primarily designed for use withpolyanhydrides. In this method, the variant B7-DC polypeptide, variantB7-DC fusion protein or nucleic acid encoding the same is dispersed ordissolved in a solution of a selected polymer in a volatile organicsolvent like methylene chloride. The mixture is then suspended in oil,such as silicon oil, by stirring, to form an emulsion. Within 24 hours,the solvent diffuses into the oil phase and the emulsion droplets hardeninto solid polymer microspheres. Unlike solvent evaporation, this methodcan be used to make microspheres from polymers with high melting pointsand a wide range of molecular weights. Microspheres having a diameterbetween one and 300 microns can be obtained with this procedure. Theexternal morphology of the spheres is highly dependent on the type ofpolymer used. In spray drying, the polymer is dissolved in methylenechloride (0.04 g/ml). A known amount of active drug is suspended (ifinsoluble) or co-dissolved (if soluble) in the polymer solution. Thesolution or the dispersion is then spray-dried. Double walledmicrospheres can be prepared according to U.S. Pat. No. 4,861,627 toMathiowitz.

Hydrogel microspheres made of gel-type polymers such as alginate orpolyphosphazines or other dicarboxylic polymers can be prepared bydissolving the polymer in an aqueous solution, suspending the materialto be incorporated into the mixture, and extruding the polymer mixturethrough a microdroplet forming device, equipped with a nitrogen gas jet.The resulting microspheres fall into a slowly stirring, ionic hardeningbath, as described, for example, by Salib, et al., PharmazeutischeIndustrie 40-11A, 1230 (1978). Chitosan microspheres can be prepared bydissolving the polymer in acidic solution and crosslinking withtripolyphosphate. For example, carboxymethylcellulose (CMC) microsphereare prepared by dissolving the polymer in an acid solution andprecipitating the microspheres with lead ions. Alginate/polyethyleneimide (PEI) can be prepared to reduce the amount of carboxyl groups onthe alginate microcapsules.

Other delivery systems including films, coatings, pellets, slabs, anddevices can be fabricated using solvent or melt casting, and extrusion,as well as standard methods for making composites. The polymer can beproduced by first mixing monomers and peptides as described by Sawhney,et al., and polymerizing the monomers with UV light. The polymerizationcan be carried out in vitro as well as in vivo.

II. Methods of Manufacture

A. Methods for Producing Variant B7-DC Polypeptides

Isolated variant B7-DC polypeptides can be obtained by, for example,chemical synthesis or by recombinant production in a host cell. Torecombinantly produce a costimulatory polypeptide, a nucleic acidcontaining a nucleotide sequence encoding the polypeptide can be used totransform, transduce, or transfect a bacterial or eukaryotic host cell(e.g., an insect, yeast, or mammalian cell). In general, nucleic acidconstructs include a regulatory sequence operably linked to a nucleotidesequence encoding a costimulatory polypeptide. Regulatory sequences(also referred to herein as expression control sequences) typically donot encode a gene product, but instead affect the expression of thenucleic acid sequences to which they are operably linked.

Useful prokaryotic and eukaryotic systems for expressing and producingpolypeptides are well know in the art include, for example, Escherichiacoli strains such as BL-21, and cultured mammalian cells such as CHOcells.

In eukaryotic host cells, a number of viral-based expression systems canbe utilized to express variant B7-DC polypeptides. Viral basedexpression systems are well known in the art and include, but are notlimited to, baculoviral, SV40, retroviral, or vaccinia based viralvectors.

Mammalian cell lines that stably express variant costimulatorypolypeptides can be produced using expression vectors with appropriatecontrol elements and a selectable marker. For example, the eukaryoticexpression vectors pCR3.1 (Invitrogen Life Technologies) and p91023(B)(see Wong et al. (1985) Science 228:810-815) are suitable for expressionof variant costimulatory polypeptides in, for example, Chinese hamsterovary (CHO) cells, COS-1 cells, human embryonic kidney 293 cells, NIH3T3cells, BHK21 cells, MDCK cells, and human vascular endothelial cells(HUVEC). Following introduction of an expression vector byelectroporation, lipofection, calcium phosphate, or calcium chlorideco-precipitation, DEAE dextran, or other suitable transfection method,stable cell lines can be selected (e.g., by antibiotic resistance toG418, kanamycin, or hygromycin). The transfected cells can be culturedsuch that the polypeptide of interest is expressed, and the polypeptidecan be recovered from, for example, the cell culture supernatant or fromlysed cells. Alternatively, a variant B7-DC polypeptide can be producedby (a) ligating amplified sequences into a mammalian expression vectorsuch as pcDNA3 (Invitrogen Life Technologies), and (b) transcribing andtranslating in vitro using wheat germ extract or rabbit reticulocytelysate.

Variant costimulatory polypeptides can be isolated using, for example,chromatographic methods such as DEAE ion exchange, gel filtration, andhydroxylapatite chromatography. For example, a costimulatory polypeptidein a cell culture supernatant or a cytoplasmic extract can be isolatedusing a protein G column. In some embodiments, variant costimulatorypolypeptides can be “engineered” to contain an amino acid sequence thatallows the polypeptides to be captured onto an affinity matrix. Forexample, a tag such as c-myc, hemagglutinin, polyhistidine, or Flag™(Kodak) can be used to aid polypeptide purification. Such tags can beinserted anywhere within the polypeptide, including at either thecarboxyl or amino terminus. Other fusions that can be useful includeenzymes that aid in the detection of the polypeptide, such as alkalinephosphatase. Immunoaffinity chromatography also can be used to purifycostimulatory polypeptides.

B. Methods for Producing Isolated Nucleic Acid Molecules

Isolated nucleic acid molecules can be produced by standard techniques,including, without limitation, common molecular cloning and chemicalnucleic acid synthesis techniques. For example, polymerase chainreaction (PCR) techniques can be used to obtain an isolated nucleic acidencoding a variant costimulatory polypeptide. PCR is a technique inwhich target nucleic acids are enzymatically amplified. Typically,sequence information from the ends of the region of interest or beyondcan be employed to design oligonucleotide primers that are identical insequence to opposite strands of the template to be amplified. PCR can beused to amplify specific sequences from DNA as well as RNA, includingsequences from total genomic DNA or total cellular RNA. Primerstypically are 14 to 40 nucleotides in length, but can range from 10nucleotides to hundreds of nucleotides in length. General PCR techniquesare described, for example in PCR Primer: A Laboratory Manual, ed. byDieffenbach and Dveksler, Cold Spring Harbor Laboratory Press, 1995.When using RNA as a source of template, reverse transcriptase can beused to synthesize a complementary DNA (cDNA) strand. Ligase chainreaction, strand displacement amplification, self-sustained sequencereplication or nucleic acid sequence-based amplification also can beused to obtain isolated nucleic acids. See, for example, Lewis (1992)Genetic Engineering News 12:1; Guatelli et al. (1990) Proc. Natl. Acad.Sci. USA 87:1874-1878; and Weiss (1991) Science 254:1292-1293.

Isolated nucleic acids can be chemically synthesized, either as a singlenucleic acid molecule or as a series of oligonucleotides (e.g., usingphosphoramidite technology for automated DNA synthesis in the 3′ to 5′direction). For example, one or more pairs of long oligonucleotides(e.g., >100 nucleotides) can be synthesized that contain the desiredsequence, with each pair containing a short segment of complementarity(e.g., about 15 nucleotides) such that a duplex is formed when theoligonucleotide pair is annealed. DNA polymerase can be used to extendthe oligonucleotides, resulting in a single, double-stranded nucleicacid molecule per oligonucleotide pair, which then can be ligated into avector. Isolated nucleic acids can also obtained by mutagenesis. B7-DCencoding nucleic acids can be mutated using standard techniques,including oligonucleotide-directed mutagenesis and/or site-directedmutagenesis through PCR. See, Short Protocols in Molecular Biology.Chapter 8, Green Publishing Associates and John Wiley & Sons, edited byAusubel et al, 1992. Examples of amino acid positions that can bemodified include those described herein.

III. Methods of Use

A. Costimulation of T Cells

Variant B7-DC polypeptides, variant B7-DC fusion proteins, nucleic acidsencoding variant B7-DC polypeptides or B7-DC fusion proteins, or cellsexpressing variant B7-DC polypeptides can be used to costimulate T cells(i.e., increase antigen-specific proliferation of T cells, enhancecytokine production by T cells, stimulate differentiation ad effectorfunctions of T cells and/or promote T cell survival).

B7-DC can bind to PD-1 (programmed cell death-1), a CD28 homolog with animmunoreceptor tyrosine-based inhibitory motifinits cytoplasmic domain(Ishida et al (1992) EMBO J. 11:3887-3895). PD-1 is expressed on asubset of thymocytes and is up-regulated on T cells, B cells, andmyeloid cells after their activation (Agata et al. (1996) Int. Immunol.8:765-772). PD-1 appears to be a negative regulator of immune responsesin vivo. For example, PD-1^(−/−) mice in the C57BL/6 background slowlydeveloped a lupus-like glomerulonephritis and progressive arthritis(Nishimura et al. (1999) Immunity 11:141-151). Additionally, PD-1^(−/−)mice in the BALB/c background rapidly developed a fatal autoimmunedilated cardiomyopathy (Nishimura et al. (2001) Science 291:319-322).Evidence also indicates, however, that B7-DC can function to costimulatea T cell response. In the presence of suboptimal TCR signals, B7-DC canstimulate increased proliferation and production of cytokines in vitro.Thus, B7-DC appears to also bind to T cell receptors other than PD-1.The experiments described in the Examples below indicate that thecostimulatory activity of B7-DC, and the variants of B7-DC describedherein, is not mediated by the PD-1 receptor.

The B7-DC variants described herein demonstrate reduced binding to PD-1relative to wild type B7-DC, yet retain the ability to costimulate Tcells. Thus, the B7-DC variants described herein retain their ability tocostimulate T cells and have a reduced ability to suppress T cellactivation by binding to PD-1. These B7-DC variants are thereforeadvantageous over wild type B7-DC for costimulating T cells. Methods forusing a variant B7-DC polypeptides and variant B7-DC fusion proteinswith reduced affinity for PD-1 to stimulate a T cell response aredisclosed herein. The methods can include contacting a T cell with aisolated variant costimulatory polypeptide. The contacting can be invitro, ex vivo, or in vivo (e.g., in a mammal such as a mouse, rat,rabbit, dog, cow, pig, non-human primate, or a human).

The contacting can occur before, during, or after activation of the Tcell. Typically, contacting of the T cell with variant costimulatorypolypeptide can be at substantially the same time as activation.Activation can be, for example, by exposing the T cell to an antibodythat binds to the T cell receptor (TCR) or one of the polypeptides ofthe CD3 complex that is physically associated with the TCR.Alternatively, a T cell can be exposed to either an alloantigen (e.g., aMHC alloantigen) on, for example, an APC [e.g., an interdigitatingdendritic cell (referred to herein as a dendritic cell), a macrophage, amonocyte, or a B cell] or an antigenic peptide produced by processing ofa protein antigen by any of the above APC and presented to the T cell byMHC molecules on the surface of the APC. The T cell can be a CD4⁺ T cellor a CD8⁺ T cell.

In some embodiments, a isolated variant costimulatory polypeptide can beadministered directly to a T cell. Alternatively, an APC such as amacrophage, monocyte, interdigitating dendritic cell (referred to hereinas a dendritic cell), or B cell can be transformed, transduced, ortransfected with a nucleic acid containing a nucleotide sequence thatencodes a variant costimulatory polypeptide, and the T cell can becontacted by the transformed, transduced, or transfected APC. Thetransformed, transduced, or transfected cell can be a cell, or a progenyof a cell that, prior to being transformed, transduced, or transfected,was obtained from the subject to which it is administered, or fromanother subject (e.g., another subject of the same species).

The variant B7-DC polypeptide can be any of those described herein,including any of the disclosed amino acid alterations, polypeptidefragments, fusion proteins and combinations thereof.

If the activation is in vitro, the variant B7-DC molecule can be boundto the floor of a relevant culture vessel, e.g. a well of a plasticmicrotiter plate.

In vitro application of the isolated variant costimulatory polypeptidescan be useful, for example, in basic scientific studies of immunemechanisms or for production of activated T cells for use in studies ofT cell function or, for example, passive immunotherapy. Furthermore,variant B7-DC polypeptides can be added to in vitro assays (e.g., T cellproliferation assays) designed to test for immunity to an antigen ofinterest in a subject from which the T cells were obtained. Addition ofvariant costimulatory polypeptides to such assays would be expected toresult in a more potent, and therefore more readily detectable, in vitroresponse. Moreover, a variant B7-DC polypeptide, or an APC transformed,transfected, or transduced with a nucleic acid encoding such apolypeptide, can be used: (a) as a positive control in an assay to testfor co-stimulatory activity in other molecules; or (b) in screeningassays for compounds useful in inhibiting T costimulation (e.g.,compounds potentially useful for treating autoimmune diseases or organgraft rejection).

B. Therapeutic Uses of B7-DC Variants

1. Conditions to be Treated

The variant B7-DC polypeptides provided herein are generally useful invivo and ex vivo as immune response-stimulating therapeutics. Ingeneral, the compositions described herein are useful for treating asubject having or being predisposed to any disease or disorder to whichthe subjects immune system mounts an immune response. The ability ofvariant B7-DC polypeptides to costimulate T cells makes the disclosedcompositions useful to stimulate or enhance immune responses involving Tcells. Thus, in a preferred embodiment, the type of disease to betreated or prevented is a malignant tumor or a chronic infectiousdisease caused by a bacterium, virus, protozoan, helminth, or othermicrobial pathogen that enters intracellularly and is attacked, i.e., bycytotoxic T lymphocytes. Costimulation of T cells using the variantB7-DC compositions described herein is also advantageous to treat orprevent conditions characterized by immunosuppression.

i. Viral Infections

Because viral infections are cleared primarily by T-cells, an increasein T-cell activity would be therapeutically useful in situations wheremore rapid or thorough clearance of an infective viral agent would bebeneficial to an animal or human subject. Thus, variant B7-DCpolypeptides and variant B7-DC fusion proteins can be administered forthe treatment of local or systemic viral infections, including, but notlimited to, immunodeficiency (e.g., HIV), papilloma (e.g., HPV), herpes(e.g., HSV), encephalitis, influenza (e.g., human influenza virus A),and common cold (e.g., human rhinovirus) viral infections. For example,pharmaceutical formulations of B7-DC compositions factors can beadministered topically to treat viral skin diseases such as herpeslesions or shingles, or genital warts. Pharmaceutical formulations ofvariant B7-DC compositions can also be administered to treat systemicviral diseases, including, but not limited to, AIDS, influenza, thecommon cold, or encephalitis.

ii. Cancer

Variant B7-DC polypeptides, variant B7-DC fusion proteins and nucleicacids encoding the same may be useful in the induction of tumorimmunity. For example, tumor cells, including, but not limited to,sarcoma, melanoma, lymphoma, leukemia, neuroblastoma, or carcinomacells, can be engineered to carry a nucleic acid encoding a variantB7-DC polypeptide or variant B7-DC fusion protein as described herein,and then administered to a subject to traverse tumor-specific tolerancein the subject. Notably, ectopic expression of B7-1 in B7 negativemurine tumor cells has been shown to induce T-cell mediated specificimmunity accompanied by tumor rejection and prolonged protection totumor challenge in mice (L. Chen et al., supra; S. Townsend et al.,supra; S. Baskar et al., supra). Tumor or cancer cell gene therapytreatments utilizing B7-related factors may be modeled on animalexperiments (see K. Dunussi-Joannopoulos et al. (1997) J. Pediatr.Hematol. Oncol. 19:356-340; K. Hiroishi et al. (1999) Gene Ther.6:1988-1994; B. K. Martin et al. (1999) J. Immunol. 162:6663-6670; M.Kuiper et al. (2000) Adv. Exp. Med. Biol. 465:381-390), or human phase Itrial experiments (H. L. Kaufman et al. (2000) Hum. Gene Ther.11:1065-1082), which use B7-1 or B7-2 for gene transfer therapy. It willbe understood that such methods may be adapted for use with varioustumor or cancer cells. Additionally, tumor immunity may be achieved byadministration of variant B7-DC polypeptides and variant B7-DC fusionproteins that directly stimulates the immune cells.

Malignant tumors which may be treated are classified herein according tothe embryonic origin of the tissue from which the tumor is derived.Carcinomas are tumors arising from endodermal or ectodermal tissues suchas skin or the epithelial lining of internal organs and glands.Sarcomas, which arise less frequently, are derived from mesodermalconnective tissues such as bone, fat, and cartilage. The leukemias andlymphomas are malignant tumors of hematopoietic cells of the bonemarrow. Leukemias proliferate as single cells, whereas lymphomas tend togrow as tumor masses. Malignant tumors may show up at numerous organs ortissues of the body to establish a cancer.

The types of cancer that can be treated in with the providedcompositions and methods include, but are not limited to, the following:bladder, brain, breast, cervical, colo-rectal, esophageal, kidney,liver, lung, nasopharangeal, pancreatic, prostate, skin, stomach,uterine, and the like. Administration is not limited to the treatment ofan existing tumor or infectious disease but can also be used to preventor lower the risk of developing such diseases in an individual i.e., forprophylactic use. Potential candidates for prophylactic vaccinationinclude individuals with a high risk of developing cancer, i.e., with apersonal or familial history of certain types of cancer.

iii. Immunosuppressed Conditions

Variant B7-DC polypeptides and variant B7-DC fusion proteins can be usedfor treatment of disease conditions characterized by immunosuppression,including, but not limited to, AIDS or AIDS-related complex, othervirally or environmentally-induced conditions, and certain congenitalimmune deficiencies. Variant B7-DC polypeptides and variant B7-DC fusionproteins can also be employed to increase immune function that has beenimpaired by the use of radiotherapy of immunosuppressive drugs (e.g.,certain chemotherapeutic agents), and therefore can be particularlyuseful when given in conjunction with such drugs or radiotherapy.

2. Use of B7-DC Variants in Vaccines

Variant B7-DC polypeptides, variant B7-DC fusion proteins, and/ornucleic acids encoding the same may be administered alone or incombination with any other suitable treatment. In one embodiment,variant B7-DC polypeptides, variant B7-DC fusion proteins, and/ornucleic acids encoding the same may be administered in conjunction with,or as a component of, a vaccine composition. Suitable components ofvaccine compositions are described above. Variant B7-DC compositionsdescribed herein can be administered prior to, concurrently with, orafter the administration of a vaccine. In one embodiment the variantB7-DC composition is administered at the same time as administration ofa vaccine.

The variant B7-DC compositions described herein may be administered inconjunction with prophylactic vaccines, which confer resistance in asubject to subsequent exposure to infectious agents, or in conjunctionwith therapeutic vaccines, which can be used to initiate or enhance asubject's immune response to a pre-existing antigen, such as a tumorantigen in a subject with cancer, or a viral antigen in a subjectinfected with a virus.

The desired outcome of a prophylactic, therapeutic or de-sensitizedimmune response may vary according to the disease, according toprinciples well known in the art. For example, an immune responseagainst an infectious agent may completely prevent colonization andreplication of an infectious agent, affecting “sterile immunity” and theabsence of any disease symptoms. However, a vaccine against infectiousagents may be considered effective if it reduces the number, severity orduration of symptoms; if it reduces the number of individuals in apopulation with symptoms; or reduces the transmission of an infectiousagent. Similarly, immune responses against cancer, allergens orinfectious agents may completely treat a disease, may alleviatesymptoms, or may be one facet in an overall therapeutic interventionagainst a disease. For example, the stimulation of an immune responseagainst a cancer may be coupled with surgical, chemotherapeutic,radiologic, hormonal and other immunologic approaches in order to affecttreatment.

C. Methods of Administration of Variant B7-DC Polypeptides

In some in vivo approaches, a variant B7-DC polypeptide or variant B7-DCfusion protein itself is administered to a subject in a therapeuticallyeffective amount. Typically, the polypeptides can be suspended in apharmaceutically-acceptable carrier. Pharmaceutically acceptablecarriers are biologically compatible vehicles (e.g., physiologicalsaline) that are suitable for administration to a human. Atherapeutically effective amount is an amount of a variant costimulatorypolypeptide that is capable of producing a medically desirable result(e.g., an enhanced T cell response) in a treated animal. Variant B7-DCpolypeptides and B7-DC fusion proteins can be administered orally or byintravenous infusion, or injected subcutaneously, intramuscularly,intraperitoneally, intrarectally, intravaginally, intranasally,intragastrically, intratracheally, or intrapulmonarily. The variantcostimulatory polypeptides can be delivered directly to an appropriatelymphoid tissue (e.g., spleen, lymph node, or mucosal-associatedlymphoid tissue).

D). Methods of Administration of Nucleic Acids and Cells

Nucleic acids encoding variant B7-DC polypeptides or fusion proteins canbe administered to subjects in need thereof. Nucleic delivery involvesintroduction of “foreign” nucleic acids into a cell and ultimately, intoa live animal. Several general strategies for gene therapy have beenstudied and have been reviewed extensively (Yang, N-S., Crit. Rev.Biotechnol. 12:335-356 (1992); Anderson, W. F., Science 256:808-813(1992); Miller, A. S., Nature 357:455-460 (1992); Crystal, R. G., Amer.J. Med. 92 (suppl 6A):44S-52S (1992); Zwiebel, J. A. et al., Ann. N.Y.Acad. Sci. 618:394-404 (1991); McLachlin, J. R. et al., Prog. Nuc. AcidRes. Molec. Biol. 38:91-135 (1990); Kohn, D. B. et al., Cancer Invest.7:179-192 (1989), which references are herein incorporated by referencein their entirety).

One approach includes nucleic acid transfer into primary cells inculture followed by autologous transplantation of the ex vivotransformed cells into the host, either systemically or into aparticular organ or tissue. In one embodiment, vectors containingnucleic acids encoding variant B7-DC polypeptides are transfected intocells that are administered to a subject in need thereof. In a preferredembodiment the cells containing the vectors containing nucleic acidsencoding variant B7-DC polypeptides are antigen presenting cells.

Ex vivo methods can include, for example, the steps of harvesting cellsfrom a subject, culturing the cells, transducing them with an expressionvector, and maintaining the cells under conditions suitable forexpression of the variant costimulatory polypeptides provided herein.These methods are known in the art of molecular biology. Thetransduction step can be accomplished by any standard means used for exvivo gene therapy, including, for example, calcium phosphate,lipofection, electroporation, viral infection, and biolistic genetransfer. Alternatively, liposomes or polymeric microparticles can beused. Cells that have been successfully transduced then can be selected,for example, for expression of the coding sequence or of a drugresistance gene. The cells then can be lethally irradiated (if desired)and injected or implanted into the subject.

In some ex vivo methods, peripheral blood mononuclear cells (PBMC) canbe withdrawn from a patient or a suitable donor and exposed ex vivo toan activating stimulus (see above) and a variant costimulatorypolypeptide (whether in soluble form or attached to a sold support bystandard methodologies). The PBMC containing highly activated T cellsthen can be introduced into the same or a different patient.

An alternative ex vivo strategy can involve transfecting or transducingcells obtained from a subject with a nucleic acid encoding a variantB7-DC polypeptide. The transfected or transduced cells then can bereturned to the subject. While such cells typically would be hemopoieticcells (e.g., bone marrow cells, macrophages, monocytes, dendritic cells,or B cells), 20 they can also be any of a wide range of types including,without limitation, fibroblasts, epithelial cells, endothelial cells,keratinocytes, or muscle cells in which they act as a source of thevariant B7-DC polypeptide for as long as they survive in the subject.The use of hemopoietic cells, including the above APC, can beparticularly useful, as such cells typically are expected to home to,among others, lymphoid tissue (e.g., lymph nodes or spleen) and thus thevariant B7-DC polypeptide can be produced in high concentration at thesite where its effect (i.e., enhancement of an immune response) isexerted. In addition, if APC are used, the APC expressing the exogenousvariant costimulatory molecule can be the same APC that present analloantigen or antigenic peptide to the relevant T cell. The variantB7-DC can be secreted by the APC or expressed on its surface.

Nucleic acid therapy can be accomplished by direct transfer of afunctionally active DNA into mammalian somatic tissue or organ in vivo.For example, nucleic acids encoding B7-DC variant polypeptides can beadministered directly to lymphoid tissues. Alternatively, lymphoidtissue specific targeting can be achieved using lymphoid tissue-specifictranscriptional regulatory elements (TREs) such as a B lymphocyte-, Tlymphocyte-, or dendritic cell-specific TRE. Lymphoid tissue specificTREs include, for example, those known in the art [see, e.g., Thompsonet al. (1992) Mol. Cell. Biol 12:1043-1053; Todd et al. (1993) J. Exp.Med. 177:1663-1674; and Penix et al. (1993) J. Exp. Med. 178:1483-1496].

DNA transfer can be achieved using a number of approaches describedbelow. These systems can be tested for successful expression in vitro byuse of a selectable marker (e.g., G418 resistance) to select transfectedclones expressing the DNA, followed by detection of the presence of theB7-H4 expression product (after treatment with the inducer in the caseof an inducible system) using an antibody to the product in anappropriate immunoassay. Efficiency of the procedure, including DNAuptake, plasmid integration and stability of integrated plasmids, can beimproved by linearizing the plasmid DNA using known methods, andco-transfection using high molecular weight mammalian DNA as a“carrier”.

Examples of successful “gene transfer” reported in the art include: (a)direct injection of plasmid DNA into mouse muscle tissues, which led toexpression of marker genes for an indefinite period of time (Wolff, J.A. et al., Science 247:1465 (1990); Acsadi, G. et al., The New Biologist3:71 (1991)); (b) retroviral vectors are effective for in vivo and insitu infection of blood vessel tissues; (c) portal vein injection anddirect injection of retrovirus preparations into liver effected genetransfer and expression in vivo (Horzaglou, M. et al., J. Biol. Chem.265:17285 (1990); Koleko, M. et al., Human Gene Therapy 2:27 (1991);Ferry, N. et al., Proc. Natl. Acad. Sci. USA 88:8387 (1991)); (d)intratracheal infusion of recombinant adenovirus into lung tissues waseffective for in vivo transfer and prolonged expression of foreign genesin lung respiratory epithelium (Rosenfeld, M. A. et al., Science 252:431(1991); (e) Herpes simplex virus vectors achieved in vivo gene transferinto brain tissue (Ahmad, F. et al., eds, Miami Short Reports—Advancesin Gene Technology: The Molecular Biology of Human Genetic Disease, Vol1, Boerringer Manneheim Biochemicals, USA, 1991).

Retroviral-mediated human therapy utilizes amphotrophic,replication-deficient retrovirus systems (Temin, H. M., Human GeneTherapy 1:111 (1990); Temin et al., U.S. Pat. No. 4,980,289; Temin etal., U.S. Pat. No. 4,650,764; Temin et al., U.S. Pat. No. 5,124,263;Wills, J. W. U.S. Pat. No. 5,175,099; Miller, A. D., U.S. Pat. No.4,861,719). Such vectors have been used to introduce functional DNA intohuman cells or tissues, for example, the adenosine deaminase gene intolymphocytes, the NPT-II gene and the gene for tumor necrosis factor intotumor infiltrating lymphocytes. Retrovirus-mediated gene deliverygenerally requires target cell proliferation for gene transfer (Miller,D. G. et al., Mol. Cell. Biol. 10:4239 (1990). This condition is met bycertain of the preferred target cells into which the present DNAmolecules are to be introduced, i.e., actively growing tumor cells. Genetherapy of cystic fibrosis using transfection by plasmids using any of anumber of methods and by retroviral vectors has been described byCollins et al., U.S. Pat. No. 5,240,846.

Nucleic acid molecules encoding variant B7-DC polypeptides or fusionproteins may be packaged into retrovirus vectors using packaging celllines that produce replication-defective retroviruses, as is well-knownin the art (see, for example, Cone, R. D. et al., Proc. Natl. Acad. Sci.USA 81:6349-6353 (1984); Mann, R. F. et al., Cell 33:153-159 (1983);Miller, A. D. et al., Molec. Cell. Biol. 5:431-437 (1985); Sorge, J., etal., Molec. Cell. Biol. 4:1730-1737 (1984); Hock, R. A. et al., Nature320:257 (1986); Miller, A. D. et al., Molec. Cell. Biol. 6:2895-2902(1986). Newer packaging cell lines which are efficient and safe for genetransfer have also been described (Bank et al., U.S. Pat. No.5,278,056).

This approach can be utilized in a site specific manner to deliver theretroviral vector to the tissue or organ of choice. Thus, for example, acatheter delivery system can be used (Nabel, E G et al., Science244:1342 (1989)). Such methods, using either a retroviral vector or aliposome vector, are particularly useful to deliver the nucleic acid tobe expressed to a blood vessel wall, or into the blood circulation of atumor.

Other virus vectors may also be used, including recombinant adenoviruses(Horowitz, M. S., In: Virology, Fields, B N et al., eds, Raven Press,New York, 1990, p. 1679; Berkner, K. L., Biotechniques 6:616 9191988),Strauss, S. E., In: The Adenoviruses, Ginsberg, H S, ed., Plenum Press,New York, 1984, chapter 11), herpes simplex virus (HSV) forneuron-specific delivery and persistence. Advantages of adenovirusvectors for human gene therapy include the fact that recombination israre, no human malignancies are known to be associated with suchviruses, the adenovirus genome is double stranded DNA which can bemanipulated to accept foreign genes of up to 7.5 kb in size, and liveadenovirus is a safe human vaccine organism. Adeno-associated virus isalso useful for human therapy (Samulski, R. J. et al., EMBO J. 10:3941(1991).

Another vector which can express the disclosed DNA molecule and isuseful in the present therapeutic setting, particularly in humans, isvaccinia virus, which can be rendered non-replicating (U.S. Pat. Nos.5,225,336; 5,204,243; 5,155,020; 4,769,330; Sutter, G et al., Proc.Natl. Acad. Sci. USA (1992) 89:10847-10851; Fuerst, T. R. et al., Proc.Natl. Acad. Sci. USA (1989) 86:2549-2553; Falkner F. G. et al.; Nucl.Acids Res (1987) 15:7192; Chakrabarti, S et al., Molec. Cell. Biol.(1985) 5:3403-3409). Descriptions of recombinant vaccinia viruses andother viruses containing heterologous DNA and their uses in immunizationand DNA therapy are reviewed in: Moss, B., Cur. Opin. Genet. Dev. (1993)3:86-90; Moss, B. Biotechnology (1992) 20: 345-362; Moss, B., Curr TopMicrobiol Immunol (1992) 158:25-38; Moss, B., Science (1991)252:1662-1667; Piccini, A et al., Adv. Virus Res. (1988) 34:43-64; Moss,B. et al., Gene Amplif Anal (1983) 3:201-213.

In addition to naked DNA or RNA, or viral vectors, engineered bacteriamay be used as vectors. A number of bacterial strains includingSalmonella, BCG and Listeria monocytogenes (LM) (Hoiseth & Stocker,Nature 291, 238-239 (1981); Poirier, T P et al. J. Exp. Med. 168, 25-32(1988); (Sadoff, J. C., et al., Science 240, 336-338 (1988); Stover, C.K., et al., Nature 351, 456-460 (1991); Aldovini, A. et al., Nature 351,479-482 (1991); Schafer, R., et al., J. Immunol. 149, 53-59 (1992);Ikonomidis, C. et al., J. Exp. Med. 180, 2209-2218 (1994)). Theseorganisms display two promising characteristics for use as vaccinevectors: (1) enteric routes of infection, providing the possibility oforal vaccine delivery; and (2) infection of monocytes/macrophagesthereby targeting antigens to professional APCs.

In addition to virus-mediated gene transfer in vivo, physical meanswell-known in the art can be used for direct transfer of DNA, includingadministration of plasmid DNA (Wolff et al., 1990, supra) andparticle-bombardment mediated gene transfer (Yang, N.-S., et al., Proc.Natl. Acad. Sci. USA 87:9568 (1990); Williams, R. S. et al., Proc. Natl.Acad. Sci. USA 88:2726 (1991); Zelenin, A. V. et al., FEBS Lett. 280:94(1991); Zelenin, A. V. et al., FEBS Lett. 244:65 (1989); Johnston, S. A.et al., In Vitro Cell. Dev. Biol. 27:11 (1991)). Furthermore,electroporation, a well-known means to transfer genes into cell invitro, can be used to transfer DNA molecules to tissues in vivo(Titomirov, A. V. et al., Biochim. Biophys. Acta 1088:131 ((1991)).

“Carrier mediated gene transfer” has also been described (Wu, C. H. etal., J. Biol. Chem. 264:16985 (1989); Wu, G. Y. et al., J. Biol. Chem.263:14621 (1988); Soriano, P. et al., Proc. Natl. Acad. Sci. USA 80:7128(1983); Wang, C-Y. et al., Proc. Natl. Acad. Sci. USA 84:7851 (1982);Wilson, J. M. et al., J. Biol. Chem. 267:963 (1992)). Preferred carriersare targeted liposomes (Nicolau, C. et al., Proc. Natl. Acad. Sci. USA80:1068 (1983); Soriano et al., supra) such as immunoliposomes, whichcan incorporate acylated mAbs into the lipid bilayer (Wang et al.,supra). Polycations such as asialoglycoprotein/polylysine (Wu et al.,1989, supra) may be used, where the conjugate includes a molecule whichrecognizes the target tissue (e.g., asialoorosomucoid for liver) and aDNA binding compound to bind to the DNA to be transfected. Polylysine isan example of a DNA binding molecule which binds DNA without damagingit. This conjugate is then complexed with plasmid DNA.

Plasmid DNA used for transfection or microinjection may be preparedusing methods well-known in the art, for example using the Quiagenprocedure (Quiagen), followed by DNA purification using known methods,such as the methods exemplified herein.

E. Dosages

For variant B7-DC polypeptides, variant B7-DC fusion proteins, nucleicacids encoding B7-DC polypeptides and variant B7-DC fusion proteins, asfurther studies are conducted, information will emerge regardingappropriate dosage levels for treatment of various conditions in variouspatients, and the ordinary skilled worker, considering the therapeuticcontext, age, and general health of the recipient, will be able toascertain proper dosing. The selected dosage depends upon the desiredtherapeutic effect, on the route of administration, and on the durationof the treatment desired. Generally dosage levels of 0.001 to 10 mg/kgof body weight daily are administered to mammals. Generally, forintravenous injection or infusion, dosage may be lower.

EXAMPLES

The present invention may be further understood by reference to thefollowing non-limiting examples.

Example 1 Molecular Modeling of B7-DC and Sequence Analysis in ThreeDimensions

Materials and Methods:

Molecular models of the Ig V-type domains of human B7-H1 (hB7-H1), mouseB7-H1 (mB7-H1), human B7-DC (hB7-DC), and mouse B7-DC (mB7-DC) weregenerated by homology (or comparative) modeling based on X-raycoordinates of human CD80 and CD86, as seen in the structures of theCD80/CTLA-4 and CD86/CTLA-4 complexes. First, the V-domains of CD80 andCD86 were optimally superimposed, and sequences of B7 family memberswere aligned based on this superimposition. The superimposition andinitial alignments were carried out using the sequence-structurealignment function of MOE (Molecular Operating Environment, ChemicalComputing Group, Montreal, Quebec, Canada). The alignment was thenmanually adjusted to match Ig consensus positions and to map otherconserved hydrophobic residues in the target sequences to core positionsin the X-ray structures. Corresponding residues in the aligned sequencesthus were predicted to have roughly equivalent spatial positions. Takingthis kind of structural information into account typically is a morereliable alignment criterion than sequence identity alone if theidentity is low, as in this case. In the aligned region, the averageidentity of the compared B7 sequences relative to the two structuraltemplates, CD80 and CD86, was only approximately 16%. The final versionof the structure-oriented sequence alignment, which provided the basisfor model building, is shown in FIG. 5. Following the alignment, coreregions of the four models were automatically assembled with MOE fromthe structural templates, and insertions and deletions in loop regionswere modeled by applying a segment matching procedure (Levitt, J. Mol.Biol., 226:507-533 (1992); and Fechteler, et al., J. Mol. Biol.,253:114-131 (1995)). Side chain replacements were carried out usingpreferred rotamer conformations seen in high-resolution protein databankstructures (Ponder and Richards, J. Mol. Biol, 193:775-791 (1987); andBerman, et al., Nucl. Acids Res., 28:235-242 (2000)). In each case,twenty intermediate models were generated, average coordinates werecalculated, and the resulting structures were energy minimized using aprotein force field (Engh and Huber, Ada Cryst., A47:392-400 (1991))until intramolecular contacts and stereochemistry of each model werereasonable. Graphical analysis of the models, including calculation ofsolvent-accessible surfaces (Connolly, J. Appl. Cryst., 16:549-558(1983)) and residue mapping studies were carried out with InsightII(Accelrys, San Diego, Calif.).

Results:

The V-regions in CD80 and CD86 share only limited sequence identity(approximately 20%), but their three-dimensional structures are verysimilar as revealed by independent crystallographic studies. Many coreor Ig superfamily consensus residue positions seen in CD80/CD86 also areconserved or conservatively replaced in other B7 family members,including B7-H1 and B7-DC (FIG. 5).

Molecular models of mouse and human B7-H1 and B7-DC molecules wereconstructed. These models revealed that in the V-regions, B7-H1 andB7-DC share more sequence identity than average across the B7family—approximately 34%. Since both B7-H1 and B7-DC bind PD-1, residueconservation could be significant for formation of the receptor bindingstructure. Therefore, the models were used to compare the putativedistribution of conserved residues that are exposed on the proteinsurface. A side-by-side comparison of these molecular models revealedsignificant conservation of surface residues on the BED faces of B7-H1and B7-DC, more so in the human than the mouse proteins. In contrast,the opposite A′GFCC′C″ faces did not display significant residueconservation. This result was somewhat unexpected because thecorresponding A′GFCC′C″ faces of both CD80 and CD86 contain theCD28/CTLA-4 binding sites.

Example 2 Mutagenesis Analysis of Receptor Binding Sites

Materials and Methods:

Mice and Cell Lines:

Female C57BL/6 (B6) mice were purchased from the National CancerInstitute (Frederick, Md.). PD-1-deficient (PD-1^(−/−)) mice weregenerated as described previously (Nishimura, et al., Int. Immunol,10:1563-1572 (1998)). Stably transfected Chinese hamster ovary (CHO)cell clones secreting fusion proteins were maintained in CHO-SF IImedium (Invitrogen Life Technologies) supplemented with 1% dialyzedfetal bovine serum (FBS; HyClone, Logan, Utah). Lymphocytes and COScells were grown in Dulbecco's modified Eagle medium (DMEM; InvitrogenLife Technologies) supplemented with 10% FBS, 25 mM HEPES, 2 mML-glutamine, 1 mM sodium pyruvate, 1% MEM nonessential amino acids, 100U/ml penicillin G, and 100 μg/ml streptomycin sulfate.

Site-directed Mutagenesis:

All variants of B7-DCIg were constructed using a two-step PCR techniqueusing B7-DCIg cDNA as a template. Overlapping oligonucleotide primerswere synthesized to encode the desired mutations, and two flanking 5′and 3′ primers were designed to contain EcoR I and Bgl II restrictionsites, respectively. Appropriate regions of the cDNAs initially wereamplified using the corresponding overlapping and flanking primers.Using the flanking 5′ and 3′ primers, fragments with overlappingsequences were fused together and amplified. PCR products were digestedwith EcoR I and Bgl II and ligated into EcoR I/Bgl II-digested pHIgvectors. To verify that the desired mutations were introduced, eachvariant was sequenced using an ABI Prism 310 Genetic Analyzer. Plasmidswere transfected into COS cells, and serum-free supernatants wereharvested and used for in vitro binding assays or isolated on a proteinG column for BIAcore analysis and functional assays.

Ig Fusion Proteins:

Fusion proteins containing the extracellular domain of mouse PD-1 linkedto the Fc portion of mouse IgG2a (PD-1Ig) were produced in stablytransfected CHO cells and isolated by protein C affinity column asdescribed previously (Wand, et al. supra). Total RNA was isolated frommouse spleen cells and B7-DC cDNA was obtained by reverse-transcriptionPCR. Murine B7-DCIg was prepared by transiently transfecting COS cellswith a plasmid containing a chimeric cDNA that included theextracellular domain of mouse B7-DC linked in frame to the CH2-CH3portion of human IgG1. Human B7-DCIg was prepared by transientlytransfecting COS cells with a plasmid containing a chimeric cDNA thatincluded the extracellular domain of human B7-DC linked in frame to theCH2-CH3 portion of human IgG1. The transfected COS cells were culturedin serum-free DMEM, and concentrated supernatants were used as sourcesof Ig fusion proteins for initial binding assays. The Ig proteins werefurther isolated on a protein G column for BIAcore analysis andfunctional assays as described previously (Wand, et al. supra).

ELISA:

A sandwich ELISA specific for B7-DCIg was established. Microtiter plateswere coated with 2 fig/ml goat anti-human IgG (Sigma, St. Louis, Mo.)overnight at 4° C. Wells were blocked for 1 hour with blocking buffer(10% FBS in PBS) and washed with PBS containing 0.05% Tween 20(PBS-Tween). COS cell culture supernatants were added and incubated for2 hours at room temperature. Known concentrations of isolated B7-DCIgalso were added to separate wells on each plate for generation of astandard curve. After extensive washing, horseradish peroxidase(HRP)-conjugated goat anti-human IgG (TACO, Inc., Burlingame, Calif.)diluted 1:2000 was added and subsequently developed with TMB substratebefore stopping the reaction by the addition of 0.5 M H₂SO₄. Absorbancewas measured at 405 mm on a microtiter plate reader. Concentrations ofvariant fusion proteins were determined by comparison with the linearrange of a standard curve of B7-DCIg. Data from triplicate wells werecollected, and the standard deviations from the mean were <10%.Experiments were repeated at least three times.

The ability of mutant and wild type B7-DCIg fusion polypeptides to bindPD-1 was measured using a capture ELISA assay. Recombinant PD-1Ig fusionproteins were coated on microtiter plates at 5 μg/ml overnight at 4° C.The plates were blocked and washed, and COS cell culture media was addedand incubated for 2 hours at room temperature. After extensive washing,HRP-conjugated goat anti-human IgG was added, followed by TMB substrateand measurement of absorbance at 405 mm.

Flow Cytometry:

Human embryonal kidney 293 cells were transfected with a PD-1 GFPvector, which was constructed by fusing GFP (green fluorescent proteincDNA) in frame to the C terminal end of a full-length mouse PD-1 cDNA.The cells were harvested 24 hours after transfection and incubated inFACS (fluorescence activated cell sorting) buffer (PBS, 3% FBS, 0.02%NaN₃) with equal amounts of fusion proteins, which had been titratedusing wild type B7-DCIg in COS cell culture media on ice for 45 minutes.An unrelated fusion protein containing human Ig was used as a negativecontrol. The cells were washed, further incubated with fluoresceinisothiocyanate (PE)-conjugated goat anti-human IgG (BioSource,Camarillo, Calif.), and analyzed on a FACScaliber (Becton Dickinson,Mountain View, Calif.) with Cell Quest software (Becton Dickinson).GFP-positive cells were gated by FL1.

Surface Plasmon Resonance Analysis:

The affinity of isolated wild type and variant B7-DC polypeptides wasanalyzed on a BIAcore™ 3000 instrument (Biacore AB, Uppsala, Sweden).All reagents except fusion proteins were purchased, pre-filtered, anddegassed from BIAcore. All experiments were performed at 25° C. using0.1 M HEPES, 0.15 M NaCl (pH 7.4) as a running buffer. Briefly, PD-1Igwas first immobilized onto a CM5 sensor chip (BIAcore) by amine couplingaccording to the BIAcore protocol. A flow cell of the CM5 chip wasderivatized through injection of a 1:1 EDC:NHS[N-ethyl-N′-(diethylaminopropyl)carbodiimide:N-hydroxysuccinimide]mixture for seven minutes, followed by injection of 20 μg/ml of PD-1Igat 10 μl/min diluted in 10 mM sodium acetate (pH 4.5). The PD-1Ig wasimmobilized at 2000 RUs. This was followed by blocking the remainingactivated carboxyl groups with 1 M ethanolamine (pH 8.5). A control flowcell was prepared in a similar fashion as above, substituting runningbuffer alone in place of PD-1Ig. The fusion proteins were diluted inrunning buffer in a concentration series of 3.75, 7.5, 15, 30, and 60μg/ml. The proteins were injected at a flow rate of 20 μl/min for 3minutes, and buffer was allowed to flow over the surface for 5 minutesfor dissociation data. The flow cells were regenerated with a single30-second pulse of 10 mM NaOH. Data analysis was performed usingBIAevaluation software package 3.1 (BIAcore).

Results:

With the aid of the molecular models, the V-domain of B7-DC was scannedfor important residues. Conserved and non-conserved residues on both theBED and A′GFCC′C″ faces were selected for site-specific mutagenesis.Residues in the mouse molecules were mutated to enable subsequentfunctional studies of selected mutant proteins. The bindingcharacteristics of the resulting variant polypeptides were assessed byspecific ELISA and FACS analysis for binding to PD-1. A total of 17mB7-DC variants were prepared and tested. The results are summarized inTable 1. Particular residues within mB7-DC were only considered to beimportant for ligand-receptor interactions if their mutation caused atleast a 50% loss of binding by FACS, or at least an order of magnitudeloss by ELISA.

Mutation of about half of these residues significantly abolished bindingto mPD-1. In particular, mB7-DC residues E71, I105, D111, and K113 wereidentified as important for binding to mPD1 Mutation of residue S58 inmB7-DC increased binding to mPD-1 as determined by ELISA. Thus, thisresidue must at least be proximal to the receptor-ligand interface andhave not only some tolerance for substitution but also potentialoptimization of binding interactions.

Variants of human B7-DC were also tested for binding to PD-1 using ELISAand FACS analysis. Mutation of hB7-DC residues K113 and D111 wereidentified as important for binding to PD-1. FACS analysis results areshown in FIG. 7.

TABLE 1 Summary of amino acid substitutions and binding characteristicsof mouse B7-DC mutants Substitutions^(b) PD-1 binding Nucleic AminoELISA Mutants^(a) Sites acids(s) acid FACS^(c) (%)^(d) B7-DC ++++ 100D33S A′ strand GAC→AGC D→S ++++ 30 S39Y B strand AGC→TAC S→Y ++++ 60E41S B strand GAG→AGC E→S ++++ 100 R56S C strand AGA→TCT R→S +++/++ 5S58Y C strand AGT→TAC S→Y ++++ 170 D65S C′ strand GAT→AGC D→S ++++ 100S67Y C′ strand TCT→TAC S→Y +++/++ 3 E71S C″ strand GAA→AGC E→S +++/++ 2R72S C″ strand AGA→AGC R→S ++++ 60 K84S D strand AAG→AGC K→S +++/++++ 13H88A E strand CAC→GCC H→A +++/++++ 20 R101S F strand CGT→AGC R→S +++ 7L103A F strand CTG→GCC L→A +++ 25 I105A F strand ATC→GCC I→A ++ 0.5D111S G strand GAC→AGC D→S ++ 0.3 K113S G strand AAG→AGC K→S −/+ <0.1T116Y G strand ACG→TAC T→Y +++/++++ 20

The PD-1 binding sites mapped to equivalent regions on the oppositeA′GFCC′C″ face. Mapping of the binding site regions revealed thatresidues whose mutation negatively (or positively) affected PD-1 bindingcould form coherent surfaces in both ligands. The proximity of importantresidues and some residues not important for binding again suggestedthat the observed effects were specific, and were not a consequence ofglobal structural changes. Comparison of important residue positionsconfirmed that the location of the putative binding sites in mB7-DCclosely corresponded to the CD28/CTLA-4 binding sites in CD86 and CD80.

Surface plasmon resonance analysis of binding of wild type and mutantproteins to PD-1 was largely consistent with the results from the FACSand ELISA analyses. The wild type B7-DC protein had an R_(max) of 227RU, and the B7-DC variant K113 did not bind to PD-1 at all (FIG. 6).These data demonstrated that wild type B7-DC had a greater steady stateaffinity for PD-1 than mutant K113. The B7-DC K113 variant showed sloweror no on- and off-rates, as compared to wild type B7-DC.

Example 3 Costimulatory Function of B7-DC Variants

Materials and Methods:

T Cell Proliferation and Cytokine Assays:

T cells from wild type B6 mice or PD-1^(−/−) mice were isolated usingnylon wool columns (Robbins Scientific Co, Sunnyvale, Calif.) asdescribed previously (Wang, et al. supra). The enriched T cells werecultured at 3×10⁵ cells per well in flat-bottomed 96-well microplatesthat were pre-coated with anti-CD3 mAb (clone 145-2C11, Pharmingen, SanDiego, Calif.) in the presence of 5 μg/ml of fusion or controlpolypeptides. Proliferation of T cells was determined by incorporationof 1 μCi/well ³H-TdR during the last 12 hours of the 3-day culture.³H-TdR incorporation was counted using a MicroBeta Trilux liquidscintillation counter (Wallac, Finland). To detect cytokine, culturesupernatants were collected at various time points, and theconcentration of IFN-γ was measured by sandwich ELISA following themanufacturer's instructions (Pharmingen).

Results:

The costimulatory potential of selected variants also was tested. B7-DCvariants K113 and D111 were selected for analysis. Both K113 and D111had minimal binding to PD-1 in both FACS and ELISA assays (Table 1). Asshown in FIGS. 8A and 8B, these variants were still able to costimulateT cell proliferation and IFN-γ production in comparison with wild typeB7-DC.

Although B7-DC might costimulate T cell growth through a yet unknownreceptor, these findings could be interpreted as an integratedstimulatory effect of unidentified costimulatory receptor(s) and PD-1.Therefore, the costimulatory effects of B7-DC variants were tested inPD-1 deficient T cells. Wild type and variant B7-DC polypeptidescostimulated proliferation of PD-1^(−/−) T cells as well as or betterthan PD-1^(+/+) cells (FIG. 9 as compared with FIG. 8A). Thus, theseobservations strongly suggest that B7-DC costimulates T cell growththrough a non-PD-1 receptor.

Example 4 Effect of Wild-type and Variant B7-DC on Growth of Tumor Cellsin Syngeneic Immunocompetent and Immunocompromised Mice

The Examples above indicate that B7-DC mutants, which lose binding toinhibitory receptor program death-1 (PD-1), retain costimulatoryfunction for T cells. These results indicate that B7-DC mutants could beapplied to enhance antitumor immune responses. Therefore, the capacityof B7-DC and B7-DC variants to stimulate antitumor immunity in wholeanimals was examined. The plasmid K113S B7-DC, which contains cDNAencoding a point mutation was transfected into a murine tumor line EG7by electroporation. EG7 cell lines which stably express K113S B7-DC wereestablished. Expression of B7-DC on the cell surface of a subline of EG7transfectants, EG7/K113S, was demonstrated by flow cytometry analysisusing specific monoclonal antibody to B7-DC. EG7 cells were alsotransfected with either parent plasmid (mock) as negative control or theplasmid containing wild type B7-DC (EG7/Wt B7-DC) as an additionalcontrol. Mock EG7 transfected cells do not express detectable B7-DCwhile wt B7-DC stable transfectants express a comparable level of B7-DCas cells stably transfected with K113S B7-DC.

Subcutaneous inoculation of EG7/K113S cells into 10 syngeneicimmunocompetent C57BL/6 mice induced transient growth of tumors asnodules. However, these tumors regressed rapidly. At day 20, all tumorsdisappeared completely. In contrast, inoculation of mock EG7 lineinduced progressively growing tumors and eventually killed the mice in30-40 days. Inoculation of mice with cells of the Wt B7-DC line alsoinduced progressively growing tumors. However, their growth was muchslower than mock EG7 line (FIG. 10).

While these results suggest that expression of K113S B7-DC on tumorcells induces regression of tumor in immune competent mice, it isunclear whether this effect is mediated by immune system. To confirmthis, K113S B7-DC cells were introduced into immune deficient nude micesubcutaneously. The results demonstrate that EG7/K113S cells has asimilar growth rate as cells of the mock line and Wt B7-DC line, andtumors did not regress (FIG. 11). These results thus demonstrate thattumor regression is mediated by the immune system and the expression ofK113S B7-DC stimulates potent immune responses.

To demonstrate that stimulation of antitumor immunity by K113S B7-DC isnot limited to EG7 tumor cells, similar experiment were performed usingstably transfected murine P815 mastocytoma cells. K113S B7-DC, parentalplasmid, as well as the plasmid containing Wt B7-DC were alsotransfected to establish control cell lines. Sublines of tumor cellsexpressing comparable levels of B7-DC were selected after flow cytometryanalysis using specific antibody as described above. Similar to theE07/K11S tumor line, subcutaneous inoculation of P815/K113S cells into10 syngeneic immunocompetent DBA/2 mice induced transient growth, andall tumors regressed rapidly. Inoculation of mock-transfected P815 cellsinduced progressively growing tumors, while injection of P815/Wt B7-DCcells also induced progressively growing tumors. However, their growthwas much slower than mock P815 line (FIG. 12). Inoculation of thesetumor lines into immune deficient nu/nu mice induced growth of tumors ata similar rate (FIG. 13), supporting that immune system plays a role ingrowth resistance of B7-DC transfectant.

Example 5 Therapeutic Effect of B7-DCIg on Tumor Growth in Mice

To determine therapeutic effect of B7-DC protein on tumor growth, micewith established P815 tumors in immune competent mice were treated withB7-DCIg fusion proteins. Inoculation of wt P815 cells into mice inducedprogressive growing tumors. Injection of mice with 0.1 mg of B7-DCIgintraperitoneally at day 3 and 8 inhibited the growth of the tumors(FIG. 14).

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of skill in the artto which the disclosed invention belongs. Publications cited herein andthe materials for which they are cited are specifically incorporated byreference.

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

I claim:
 1. An immunogenic composition for inducing an immune responseagainst a cancer antigen, comprising (a) an antigen from a tumor cell,and (b) a variant B7-DC polypeptide, wherein the variant B7-DCpolypeptide is an isolated variant of a wildtype human B7-DC polypeptidecomprising an IgV domain of B7-DC comprising an amino acid substitutionin the A′, B, C, C′, C″, D, E, F, or G β-strand of the wild-type humanB7-DC polypeptide, and has altered affinity for PD-1 compared to thewild-type human B7-DC polypeptide.
 2. The immunogenic composition ofclaim 1, wherein the variant B7-DC polypeptide is B7-DC fusion protein.3. The immunogenic composition of claim 1, wherein the isolated variantB7-DC polypeptide comprises the extracellular domain of human B7-DC. 4.The immunogenic composition of claim 1, wherein the variant B7-DCpolypeptide has decreased binding affinity for PD-1compared to thewild-type B7-DC polypeptide.
 5. The immunogenic composition of claim 2,wherein the variant B7-DC fusion protein comprises a first fusionpartner comprising the variant human B7-DC polypeptide of (b), and asecond fusion partner, comprising one or more domains of an Ig heavychain constant region.
 6. The immunogenic composition of claim 5,wherein the second fusion partner of the variant B7-DC fusion proteincomprises an amino acid sequence corresponding to the hinge, C_(H)2 andC_(H)3 regions of a human immunoglobulin chain.
 7. The immunogeniccomposition of claim 6, wherein the first fusion partner comprises theextracellular domain of the variant B7-DC, and wherein the secondpolypeptide comprises an amino acid sequence corresponding to the hinge,C_(H)2 and C_(H)3 regions of a human immunoglobulin chain.
 8. Theimmunogenic composition of claim 1, wherein the antigen is selected fromthe group consisting of peptides, proteins, polysaccharides,saccharides, lipids, and combinations thereof.
 9. The immunogeniccomposition of claim 1, wherein the antigen is an epitope of apolypeptide encoded by a nucleic acid.
 10. The immunogenic compositionof claim 1, wherein the antigen is selected from the group consisting ofalpha-actinin-4, Bcr-Ab1 fusion protein, Casp-8, beta-catenin, cdc27,cdk4, cdkn2a, coa-1, dek-can fusion protein, EF2, ETV6-AML1 fusionprotein, LDLR-fucosyltransferase, AS fusion protein, HLA-A2, HLA-A11,hsp70-2, KIAA0205, Mart2, Mum-1,2, and 3, neo-PAP, myosin class I, OS-9,pm1-RARα fusion protein, PTPRK, K-ras, N-ras, Triosephosphate isomeras,Bage-1, Gage 3,4,5,6,7, GnTV, Herv-K -mel, Lage-1, Mage-A1,2,3,4,6,10,12, Mage-C2, NA-88, NY-Eso-1/Lage-2, SP17, SSX-2, andTRP2-Int 2, MelaA (MART-I), gp100 (Pmel 17), tyrosinase, TRP-1, TRP-2,MAGE -1, MAGE-3, BAGE, GAGE-1, GAGE-2, p15(58), CEA, RAGE, NY-ESO(LAGE), SCP-1, Hom/Mel-40, PRAME, p53, H-Ras, HER-2/neu, BCR-ABL,E2A-PRL, H4-RET, IGH-IGK, MYL-RAR, Epstein Barr virus antigens, EBNA,human papillomavirus (HPV) antigens E6 and E7, TSP-180, MAGE-4, MAGE-5,MAGE-6, p185erbB2, p180erbB-3, c-met, nm-23H1, PSA, TAG-72-4, CA 19-9,CA 72-4, CAM 17.1, NuMa, K-ras, β-Catenin, CDK4, Mum-1, p16, TAGE, PSMA,PSCA, CT7, telomerase, 43-9F, 5T4, 791Tgp72, α-fetoprotein, 13HCG,BCA225, BTAA, CA 125, CA 15-3 (CA 27.29\BCAA), CA 195, CA 242, CA-50,CAM43, CD68\KP1, CO-029, FGF-5, G250, Ga733 (EpCAM), HTgp-175, M344,MA-50, MG7-Ag, MOV18, NB\70K, NY-CO-1, RCAS1, SDCCAG16, TA-90 (Mac-2binding protein\cyclophilin C -associated protein), TAAL6, TAG72, TLP,and TPS.
 11. A method for inducing an immune response to a cancerantigen in a human subject comprising administering to the subject theimmunogenic composition of claim
 1. 12. The immunogenic composition ofclaim 1, wherein the substitution in the variant B7-DC polypeptide of(b) comprises replacing the amino acid residue corresponding to aminoacid position 111numbered from the initiation methionine of wild-typehuman B7-DC (SEQ ID NO:1).
 13. The immunogenic composition of claim 12,wherein the amino acid substitution is with a serine residue.
 14. Theimmunogenic composition of claim 1, wherein the substitution in thevariant B7-DC polypeptide of (b) comprises replacing the amino acidresidue corresponding to amino acid position 113numbered from theinitiation methionine of wild-type human B7-DC (SEQ ID NO:1).
 15. Theimmunogenic composition of claim 14, wherein the substitution is with aserine residue.
 16. The immunogenic composition of claim 1, wherein thesubstitution in the variant B7-DC polypeptide of (b) comprises replacingthe amino acid residue corresponding to amino acid position 56 numberedfrom the initiation methionine of wild-type human B7-DC (SEQ ID NO:1).17. The immunogenic composition of claim 16, wherein the substitution iswith a serine residue.
 18. The immunogenic composition of claim 1,wherein the substitution in the variant B7-DC polypeptide of (b)comprises replacing the amino acid residue corresponding to amino acidposition 67 numbered from the initiation methionine of wild-type humanB7-DC (SEQ ID NO:1).
 19. The immunogenic composition of claim 18,wherein the substitution is with a tyrosine.
 20. The immunogeniccomposition of claim 1, wherein the substitution in the variant B7-DCpolypeptide of (b) comprises replacing the amino acid residuecorresponding to amino acid position 71 numbered from the initiationmethionine of wild-type human B7-DC (SEQ ID NO:1).
 21. The immunogeniccomposition of claim 20, wherein the substitution is with a serineresidue.
 22. The immunogenic composition of claim 1, wherein thesubstitution in the variant B7-DC polypeptide of (b) comprises replacingthe amino acid residue corresponding to amino acid position 101 numberedfrom the initiation methionine of wild-type human B7-DC (SEQ ID NO:1).23. The immunogenic composition of claim 22, wherein the substitution iswith a serine residue.
 24. The immunogenic composition of claim 1,wherein the substitution in the variant B7-DC polypeptide of (b)comprises replacing the amino acid residue corresponding to amino acidposition 105 numbered from the initiation methionine of wild-type humanB7-DC (SEQ ID NO:1).
 25. The immunogenic composition of claim 24,wherein the substitution is with an alanine.
 26. The immunogeniccomposition of claim 1, wherein the isolated variant B7-DC polypeptidehas increased binding affinity for PD-1 compared to wild-type B7-DCpolypeptide.
 27. An immunogenic composition for inducing an immuneresponse against a soluble antigen, comprising (a) the soluble antigen,and (b) a variant B7-DC polypeptide, wherein the variant B7-DCpolypeptide is an isolated variant of a wildtype human B7-DC polypeptidecomprising an IgV domain of B7-DC comprising an amino acid substitutionin the A′, B, C, C′, C″, D, E, F, or G β-strand of the wild-type humanB7-DC polypeptide, and has altered affinity for PD-1 compared to thewild-type human B7-DC polypeptide.
 28. The immunogenic composition ofclaim 27, wherein the B7-DC polypeptide is a B7-DC fusion protein. 29.The immunogenic composition of claim 27 , wherein the B7-DC polypeptidecomprises the extracellular domain of human B7-DC.
 30. The immunogeniccomposition of claim 27, wherein the B7-DC polypeptide has decreasedbinding affinity for PD-1compared to the wild-type B7-DC polypeptide.31. The immunogenic composition of claim 28, wherein the B7-DC fusionprotein comprises a first fusion partner comprising the human B7-DCpolypeptide of (b), and a second fusion partner, comprising one or moredomains of an Ig heavy chain constant region.
 32. The immunogeniccomposition of claim 31, wherein the second fusion partner of the B7-DCfusion protein comprises an amino acid sequence corresponding to thehinge, C_(H)2 and C_(H)3 regions of a human immunoglobulin chain. 33.The immunogenic composition of claim 32, wherein the first fusionpartner comprises the extracellular domain of B7-DC, and wherein thesecond polypeptide comprises an amino acid sequence corresponding to thehinge, C_(H)2 and C_(H)3 regions of a human immunoglobulin chain. 34.The immunogenic composition of claim 27, wherein the antigen is selectedfrom the group consisting of peptides, proteins, polysaccharides,saccharides, and combinations thereof.
 35. The immunogenic compositionof claim 27, wherein the antigen is an epitope of a polypeptide encodedby a nucleic acid.
 36. The immunogenic composition of claim 27, whereinthe antigen is derived from a virus, bacterium, parasite, plant,protozoan, fungus, tissue, transformed cell, allergen, environmentalantigen, or tumor antigen.
 37. The immunogenic composition of claim 27,wherein the antigen is selected from the group consisting ofalpha-actinin-4, Bcr-Ab1 fusion protein, Casp-8, beta-catenin, cdc27,cdk4, cdkn2a, coa-1, dek-can fusion protein, EF2, ETV6-AML1 fusionprotein, LDLR-fucosyltransferase, AS fusion protein, HLA-A2, HLA-A11,hsp70-2, KIAA0205, Mart2, Mum-1,2, and 3, neo-PAP, myosin class I, OS-9,pm1-RARα fusion protein, PTPRK, K-ras, N-ras, Triosephosphate isomeras,Bage-1, Gage 3,4,5,6,7, GnTV, Herv-K-mel, Lage-1, Mage-A1,2,3,4,6,10,12, Mage-C2, NA-88, NY-Eso-1/Lage-2, SP17, SSX-2, andTRP2-Int 2, MelaA (MART-I), gp100 (Pmel 17), tyrosinase, TRP-1, TRP-2,MACE -1, MAGE-3, BAGE, GAGE-1, GAGE-2, p15(58), CEA, RAGE, NY-ESO(LAGE), SCP-1, Hom/Mel-40, PRAME, p53, H-Ras, HER-2/neu, BCR-ABL,E2A-PRL, H4-RET, IGH-IGK, MYL-RAR, Epstein Barr virus antigens, EBNA,human papillomavirus (HPV) antigens E6 and E7, TSP-180, MAGE-4, MAGE-5,MAGE-6, p185erbB2, p180erbB-3, c-met, nm-23H1, PSA, TAG-72-4, CA 19-9,CA 72-4, CAM 17.1, NuMa, K-ras, β-Catenin, CDK4, Mum-1, p16, TAGE, PSMA,PSCA, CT7, telomerase, 43-9F, 5T4, 791Tgp72, α-fetoprotein, 13HCG,BCA225, BTAA, CA 125, CA 15-3 (CA 27.29\BCAA), CA 195, CA 242, CA-50,CAM43, CD68\KP1, CO-029, FGF-5, G250, Ga733 (EpCAM), HTgp-175, M344,MA-50, MG7-Ag, MOV18, NB\70K, NY-CO-1, RCAS1, SDCCAG16, TA-90 (Mac-2binding protein\cyclophilin C -associated protein), TAAL6, TAG72, TLP,and TPS.
 38. The immunogenic composition of claim 27, wherein thesubstitution in the variant B7-DC polypeptide of (b) comprises replacingthe amino acid residue corresponding to amino acid position 111 numberedfrom the initiation methionine of wild-type human B7-DC (SEQ ID NO:1).39. The immunogenic composition of claim 38, wherein the amino acidsubstitution is with a serine residue.
 40. The immunogenic compositionof claim 27, wherein the substitution in the variant B7-DC polypeptideof (b) comprises replacing the amino acid residue corresponding to aminoacid position 113 numbered from the initiation methionine of wild-typehuman B7-DC (SEQ ID NO:1).
 41. The immunogenic composition of claim 40,wherein the substitution is with a serine residue.
 42. The immunogeniccomposition of claim 27, wherein the substitution in the variant B7-DCpolypeptide of (b) comprises replacing the amino acid residuecorresponding to amino acid position 56 numbered from the initiationmethionine of wild-type human B7-DC (SEQ ID NO:1).
 43. The immunogeniccomposition of claim 42, wherein the substitution is with a serineresidue.
 44. The immunogenic composition of claim 27, wherein thesubstitution in the variant B7-DC polypeptide of (b) comprises replacingthe amino acid residue corresponding to amino acid position 67 numberedfrom the initiation methionine of wild-type human B7-DC (SEQ ID NO:1).45. The immunogenic composition of claim 44, wherein the substitution iswith a tyrosine.
 46. The immunogenic composition of claim 27, whereinthe substitution in the variant B7-DC polypeptide of (b) comprisesreplacing the amino acid residue corresponding to amino acid position 71numbered from the initiation methionine of wild-type human B7-DC (SEQ IDNO:1).
 47. The immunogenic composition of claim 46, wherein thesubstitution is with a serine residue.
 48. The immunogenic compositionof claim 27, wherein the substitution in the variant B7-DC polypeptideof (b) comprises replacing the amino acid residue corresponding to aminoacid position 101 numbered from the initiation methionine of wild-typehuman B7-DC (SEQ ID NO:1).
 49. The immunogenic composition of claim 48,wherein the substitution is with a serine residue.
 50. The immunogeniccomposition of claim 27, wherein the substitution in the variant B7-DCpolypeptide of (b) comprises replacing the amino acid residuecorresponding to amino acid position 105 numbered from the initiationmethionine of wild-type human B7-DC (SEQ ID NO:1).
 51. The immunogeniccomposition of claim 50, wherein the substitution is with an alanine.52. The immunogenic composition of claim 27, wherein the isolatedvariant B7-DC polypeptide has increased binding affinity for PD-1compared to wild-type B7-DC polypeptide.
 53. A method for inducing animmune response to a soluble antigen in a human subject comprisingadministering to the subject the immunogenic composition of claim 27.